Consistent use of @Nullable across the codebase (even for internals)

Beyond just formally declaring the current behavior, this revision actually enforces non-null behavior in selected signatures now, not tolerating null values anymore when not explicitly documented. It also changes some utility methods with historic null-in/null-out tolerance towards enforced non-null return values, making them a proper citizen in non-null assignments.

Some issues are left as to-do: in particular a thorough revision of spring-test, and a few tests with unclear failures (ignored as "TODO: NULLABLE") to be sorted out in a follow-up commit.

Issue: SPR-15540

spring-core/src/main/java/org/springframework/core/BridgeMethodResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -57,9 +57,10 @@ public abstract class BridgeMethodResolver {
 	 * if no more specific one could be found)
 	 */
 	public static Method findBridgedMethod(Method bridgeMethod) {
-		if (bridgeMethod == null || !bridgeMethod.isBridge()) {
+		if (!bridgeMethod.isBridge()) {
 			return bridgeMethod;
 		}
+
 		// Gather all methods with matching name and parameter size.
 		List<Method> candidateMethods = new ArrayList<>();
 		Method[] methods = ReflectionUtils.getAllDeclaredMethods(bridgeMethod.getDeclaringClass());
@@ -68,10 +69,12 @@ public abstract class BridgeMethodResolver {
 				candidateMethods.add(candidateMethod);
 			}
 		}
+
 		// Now perform simple quick check.
 		if (candidateMethods.size() == 1) {
 			return candidateMethods.get(0);
 		}
+
 		// Search for candidate match.
 		Method bridgedMethod = searchCandidates(candidateMethods, bridgeMethod);
 		if (bridgedMethod != null) {
@@ -104,7 +107,7 @@ public abstract class BridgeMethodResolver {
 	 * @return the bridged method, or {@code null} if none found
 	 */
 	@Nullable
-	private static Method searchCandidates(@Nullable List<Method> candidateMethods, Method bridgeMethod) {
+	private static Method searchCandidates(List<Method> candidateMethods, Method bridgeMethod) {
 		if (candidateMethods.isEmpty()) {
 			return null;
 		}

spring-core/src/main/java/org/springframework/core/CollectionFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -91,7 +91,7 @@ public abstract class CollectionFactory {
 	 * @param collectionType the collection type to check
 	 * @return {@code true} if the type is <em>approximable</em>
 	 */
-	public static boolean isApproximableCollectionType(Class<?> collectionType) {
+	public static boolean isApproximableCollectionType(@Nullable Class<?> collectionType) {
 		return (collectionType != null && approximableCollectionTypes.contains(collectionType));
 	}
 
@@ -216,7 +216,7 @@ public abstract class CollectionFactory {
 	 * @param mapType the map type to check
 	 * @return {@code true} if the type is <em>approximable</em>
 	 */
-	public static boolean isApproximableMapType(Class<?> mapType) {
+	public static boolean isApproximableMapType(@Nullable Class<?> mapType) {
 		return (mapType != null && approximableMapTypes.contains(mapType));
 	}
 
@@ -334,6 +334,7 @@ public abstract class CollectionFactory {
 	public static Properties createStringAdaptingProperties() {
 		return new Properties() {
 			@Override
+			@Nullable
 			public String getProperty(String key) {
 				Object value = get(key);
 				return (value != null ? value.toString() : null);

spring-core/src/main/java/org/springframework/core/ConfigurableObjectInputStream.java

@@ -46,7 +46,7 @@ public class ConfigurableObjectInputStream extends ObjectInputStream {
 	 * @param classLoader the ClassLoader to use for loading local classes
 	 * @see java.io.ObjectInputStream#ObjectInputStream(java.io.InputStream)
 	 */
-	public ConfigurableObjectInputStream(InputStream in, ClassLoader classLoader) throws IOException {
+	public ConfigurableObjectInputStream(InputStream in, @Nullable ClassLoader classLoader) throws IOException {
 		this(in, classLoader, true);
 	}
 
@@ -59,7 +59,7 @@ public class ConfigurableObjectInputStream extends ObjectInputStream {
 	 * @see java.io.ObjectInputStream#ObjectInputStream(java.io.InputStream)
 	 */
 	public ConfigurableObjectInputStream(
-			InputStream in, ClassLoader classLoader, boolean acceptProxyClasses) throws IOException {
+			InputStream in, @Nullable ClassLoader classLoader, boolean acceptProxyClasses) throws IOException {
 
 		super(in);
 		this.classLoader = classLoader;

spring-core/src/main/java/org/springframework/core/Conventions.java

@@ -181,12 +181,10 @@ public abstract class Conventions {
 	 * method, taking the generic collection type, if any, into account, falling
 	 * back on the given return value if the method declaration is not specific
 	 * enough, e.g. {@code Object} return type or untyped collection.
-	 *
 	 * <p>As of 5.0 this method supports reactive types:<br>
 	 * {@code Mono<com.myapp.Product>} becomes {@code "productMono"}<br>
 	 * {@code Flux<com.myapp.MyProduct>} becomes {@code "myProductFlux"}<br>
 	 * {@code Observable<com.myapp.MyProduct>} becomes {@code "myProductObservable"}<br>
-	 *
 	 * @param method the method to generate a variable name for
 	 * @param resolvedType the resolved return type of the method
 	 * @param value the return value (may be {@code null} if not available)
@@ -230,12 +228,11 @@ public abstract class Conventions {
 		}
 		else {
 			valueClass = resolvedType;
-
 			if (reactiveAdapterRegistry.hasAdapters()) {
 				ReactiveAdapter adapter = reactiveAdapterRegistry.getAdapter(valueClass);
 				if (adapter != null && !adapter.getDescriptor().isNoValue()) {
 					reactiveSuffix = ClassUtils.getShortName(valueClass);
-					valueClass = ResolvableType.forMethodReturnType(method).getGeneric(0).resolve();
+					valueClass = ResolvableType.forMethodReturnType(method).getGeneric().resolve(Object.class);
 				}
 			}
 		}

spring-core/src/main/java/org/springframework/core/DecoratingClassLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.util.Collections;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -53,7 +54,7 @@ public abstract class DecoratingClassLoader extends ClassLoader {
 	 * Create a new DecoratingClassLoader using the given parent ClassLoader
 	 * for delegation.
 	 */
-	public DecoratingClassLoader(ClassLoader parent) {
+	public DecoratingClassLoader(@Nullable ClassLoader parent) {
 		super(parent);
 	}
 

spring-core/src/main/java/org/springframework/core/GenericTypeResolver.java

@@ -111,6 +111,7 @@ public abstract class GenericTypeResolver {
 		return getSingleGeneric(resolvableType);
 	}
 
+	@Nullable
 	private static Class<?> getSingleGeneric(ResolvableType resolvableType) {
 		Assert.isTrue(resolvableType.getGenerics().length == 1,
 				() -> "Expected 1 type argument on generic interface [" + resolvableType +
@@ -146,14 +147,16 @@ public abstract class GenericTypeResolver {
 	 * @return the resolved type (possibly the given generic type as-is)
 	 * @since 5.0
 	 */
-	@Nullable
-	public static Type resolveType(Type genericType, Class<?> contextClass) {
+	public static Type resolveType(Type genericType, @Nullable Class<?> contextClass) {
 		if (contextClass != null) {
 			if (genericType instanceof TypeVariable) {
 				ResolvableType resolvedTypeVariable = resolveVariable(
 						(TypeVariable<?>) genericType, ResolvableType.forClass(contextClass));
 				if (resolvedTypeVariable != ResolvableType.NONE) {
-					return resolvedTypeVariable.resolve();
+					Class<?> resolved = resolvedTypeVariable.resolve();
+					if (resolved != null) {
+						return resolved;
+					}
 				}
 			}
 			else if (genericType instanceof ParameterizedType) {
@@ -178,7 +181,10 @@ public abstract class GenericTypeResolver {
 							generics[i] = ResolvableType.forType(typeArgument).resolve();
 						}
 					}
-					return ResolvableType.forClassWithGenerics(resolvedType.getRawClass(), generics).getType();
+					Class<?> rawClass = resolvedType.getRawClass();
+					if (rawClass != null) {
+						return ResolvableType.forClassWithGenerics(rawClass, generics).getType();
+					}
 				}
 			}
 		}
@@ -242,8 +248,9 @@ public abstract class GenericTypeResolver {
 	@SuppressWarnings("rawtypes")
 	private static void buildTypeVariableMap(ResolvableType type, Map<TypeVariable, Type> typeVariableMap) {
 		if (type != ResolvableType.NONE) {
-			if (type.getType() instanceof ParameterizedType) {
-				TypeVariable<?>[] variables = type.resolve().getTypeParameters();
+			Class<?> resolved = type.resolve();
+			if (resolved != null && type.getType() instanceof ParameterizedType) {
+				TypeVariable<?>[] variables = resolved.getTypeParameters();
 				for (int i = 0; i < variables.length; i++) {
 					ResolvableType generic = type.getGeneric(i);
 					while (generic.getType() instanceof TypeVariable<?>) {
@@ -258,8 +265,8 @@ public abstract class GenericTypeResolver {
 			for (ResolvableType interfaceType : type.getInterfaces()) {
 				buildTypeVariableMap(interfaceType, typeVariableMap);
 			}
-			if (type.resolve().isMemberClass()) {
-				buildTypeVariableMap(ResolvableType.forClass(type.resolve().getEnclosingClass()), typeVariableMap);
+			if (resolved != null && resolved.isMemberClass()) {
+				buildTypeVariableMap(ResolvableType.forClass(resolved.getEnclosingClass()), typeVariableMap);
 			}
 		}
 	}

spring-core/src/main/java/org/springframework/core/LocalVariableTableParameterNameDiscoverer.java

@@ -35,6 +35,7 @@ import org.springframework.asm.MethodVisitor;
 import org.springframework.asm.Opcodes;
 import org.springframework.asm.SpringAsmInfo;
 import org.springframework.asm.Type;
+import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 
 /**
@@ -157,6 +158,7 @@ public class LocalVariableTableParameterNameDiscoverer implements ParameterNameD
 		}
 
 		@Override
+		@Nullable
 		public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
 			// exclude synthetic + bridged && static class initialization
 			if (!isSyntheticOrBridged(access) && !STATIC_CLASS_INIT.equals(name)) {

spring-core/src/main/java/org/springframework/core/MethodClassKey.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -76,7 +76,7 @@ public final class MethodClassKey implements Comparable<MethodClassKey> {
 		int result = this.method.getName().compareTo(other.method.getName());
 		if (result == 0) {
 			result = this.method.toString().compareTo(other.method.toString());
-			if (result == 0 && this.targetClass != null) {
+			if (result == 0 && this.targetClass != null && other.targetClass != null) {
 				result = this.targetClass.getName().compareTo(other.targetClass.getName());
 			}
 		}

spring-core/src/main/java/org/springframework/core/MethodIntrospector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -52,7 +52,7 @@ public abstract class MethodIntrospector {
 	 * @return the selected methods associated with their metadata (in the order of retrieval),
 	 * or an empty map in case of no match
 	 */
-	public static <T> Map<Method, T> selectMethods(Class<?> targetType, @Nullable final MetadataLookup<T> metadataLookup) {
+	public static <T> Map<Method, T> selectMethods(Class<?> targetType, final MetadataLookup<T> metadataLookup) {
 		final Map<Method, T> methodMap = new LinkedHashMap<>();
 		Set<Class<?>> handlerTypes = new LinkedHashSet<>();
 		Class<?> specificHandlerType = null;
@@ -66,16 +66,13 @@ public abstract class MethodIntrospector {
 		for (Class<?> currentHandlerType : handlerTypes) {
 			final Class<?> targetClass = (specificHandlerType != null ? specificHandlerType : currentHandlerType);
 
-			ReflectionUtils.doWithMethods(currentHandlerType, new ReflectionUtils.MethodCallback() {
-				@Override
-				public void doWith(Method method) {
-					Method specificMethod = ClassUtils.getMostSpecificMethod(method, targetClass);
-					T result = metadataLookup.inspect(specificMethod);
-					if (result != null) {
-						Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
-						if (bridgedMethod == specificMethod || metadataLookup.inspect(bridgedMethod) == null) {
-							methodMap.put(specificMethod, result);
-						}
+			ReflectionUtils.doWithMethods(currentHandlerType, method -> {
+				Method specificMethod = ClassUtils.getMostSpecificMethod(method, targetClass);
+				T result = metadataLookup.inspect(specificMethod);
+				if (result != null) {
+					Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
+					if (bridgedMethod == specificMethod || metadataLookup.inspect(bridgedMethod) == null) {
+						methodMap.put(specificMethod, result);
 					}
 				}
 			}, ReflectionUtils.USER_DECLARED_METHODS);
@@ -93,12 +90,8 @@ public abstract class MethodIntrospector {
 	 * @return the selected methods, or an empty set in case of no match
 	 */
 	public static Set<Method> selectMethods(Class<?> targetType, final ReflectionUtils.MethodFilter methodFilter) {
-		return selectMethods(targetType, new MetadataLookup<Boolean>() {
-			@Override
-			public Boolean inspect(Method method) {
-				return (methodFilter.matches(method) ? Boolean.TRUE : null);
-			}
-		}).keySet();
+		return selectMethods(targetType,
+				(MetadataLookup<Boolean>) method -> (methodFilter.matches(method) ? Boolean.TRUE : null)).keySet();
 	}
 
 	/**

spring-core/src/main/java/org/springframework/core/MethodParameter.java

@@ -378,7 +378,7 @@ public class MethodParameter {
 	/**
 	 * Set a resolved (generic) parameter type.
 	 */
-	void setParameterType(Class<?> parameterType) {
+	void setParameterType(@Nullable Class<?> parameterType) {
 		this.parameterType = parameterType;
 	}
 
@@ -408,7 +408,7 @@ public class MethodParameter {
 	public Type getGenericParameterType() {
 		if (this.genericParameterType == null) {
 			if (this.parameterIndex < 0) {
-				this.genericParameterType = (this.method != null ? this.method.getGenericReturnType() : null);
+				this.genericParameterType = (this.method != null ? this.method.getGenericReturnType() : void.class);
 			}
 			else {
 				this.genericParameterType = (this.method != null ?
@@ -489,7 +489,8 @@ public class MethodParameter {
 	 */
 	@Nullable
 	public <A extends Annotation> A getMethodAnnotation(Class<A> annotationType) {
-		return adaptAnnotation(getAnnotatedElement().getAnnotation(annotationType));
+		A annotation = getAnnotatedElement().getAnnotation(annotationType);
+		return (annotation != null ? adaptAnnotation(annotation) : null);
 	}
 
 	/**
@@ -560,7 +561,7 @@ public class MethodParameter {
 	 * this point; it just allows discovery to happen when the application calls
 	 * {@link #getParameterName()} (if ever).
 	 */
-	public void initParameterNameDiscovery(ParameterNameDiscoverer parameterNameDiscoverer) {
+	public void initParameterNameDiscovery(@Nullable ParameterNameDiscoverer parameterNameDiscoverer) {
 		this.parameterNameDiscoverer = parameterNameDiscoverer;
 	}
 
@@ -720,22 +721,28 @@ public class MethodParameter {
 		 */
 		public static boolean isNullable(MethodParameter param) {
 			if (param.getContainingClass().isAnnotationPresent(Metadata.class)) {
-				int parameterIndex = param.getParameterIndex();
-				if (parameterIndex == -1) {
-					KFunction<?> function = ReflectJvmMapping.getKotlinFunction(param.getMethod());
+				Method method = param.getMethod();
+				Constructor<?> ctor = param.getConstructor();
+				int index = param.getParameterIndex();
+				if (method != null && index == -1) {
+					KFunction<?> function = ReflectJvmMapping.getKotlinFunction(method);
 					return (function != null && function.getReturnType().isMarkedNullable());
 				}
 				else {
-					KFunction<?> function = (param.getMethod() != null ?
-							ReflectJvmMapping.getKotlinFunction(param.getMethod()) :
-							ReflectJvmMapping.getKotlinFunction(param.getConstructor()));
+					KFunction<?> function = null;
+					if (method != null) {
+						function = ReflectJvmMapping.getKotlinFunction(method);
+					}
+					else if (ctor != null) {
+						function = ReflectJvmMapping.getKotlinFunction(ctor);
+					}
 					if (function != null) {
 						List<KParameter> parameters = function.getParameters();
 						return parameters
 								.stream()
 								.filter(p -> KParameter.Kind.VALUE.equals(p.getKind()))
 								.collect(Collectors.toList())
-								.get(parameterIndex)
+								.get(index)
 								.getType()
 								.isMarkedNullable();
 					}

spring-core/src/main/java/org/springframework/core/NestedCheckedException.java

@@ -62,7 +62,7 @@ public abstract class NestedCheckedException extends Exception {
 	 * @param msg the detail message
 	 * @param cause the nested exception
 	 */
-	public NestedCheckedException(String msg, Throwable cause) {
+	public NestedCheckedException(@Nullable String msg, @Nullable Throwable cause) {
 		super(msg, cause);
 	}
 
@@ -72,6 +72,7 @@ public abstract class NestedCheckedException extends Exception {
 	 * if there is one.
 	 */
 	@Override
+	@Nullable
 	public String getMessage() {
 		return NestedExceptionUtils.buildMessage(super.getMessage(), getCause());
 	}
@@ -106,7 +107,7 @@ public abstract class NestedCheckedException extends Exception {
 	 * @param exType the exception type to look for
 	 * @return whether there is a nested exception of the specified type
 	 */
-	public boolean contains(Class<?> exType) {
+	public boolean contains(@Nullable Class<?> exType) {
 		if (exType == null) {
 			return false;
 		}

spring-core/src/main/java/org/springframework/core/NestedExceptionUtils.java

@@ -40,7 +40,8 @@ public abstract class NestedExceptionUtils {
 	 * @param cause the root cause
 	 * @return the full exception message
 	 */
-	public static String buildMessage(String message, Throwable cause) {
+	@Nullable
+	public static String buildMessage(@Nullable String message, @Nullable Throwable cause) {
 		if (cause == null) {
 			return message;
 		}
@@ -59,7 +60,7 @@ public abstract class NestedExceptionUtils {
 	 * @since 4.3.9
 	 */
 	@Nullable
-	public static Throwable getRootCause(Throwable original) {
+	public static Throwable getRootCause(@Nullable Throwable original) {
 		if (original == null) {
 			return null;
 		}

spring-core/src/main/java/org/springframework/core/NestedIOException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,8 @@ package org.springframework.core;
 
 import java.io.IOException;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Subclass of {@link IOException} that properly handles a root cause,
  * exposing the root cause just like NestedChecked/RuntimeException does.
@@ -59,7 +61,7 @@ public class NestedIOException extends IOException {
 	 * @param msg the detail message
 	 * @param cause the nested exception
 	 */
-	public NestedIOException(String msg, Throwable cause) {
+	public NestedIOException(@Nullable String msg, @Nullable Throwable cause) {
 		super(msg, cause);
 	}
 
@@ -69,6 +71,7 @@ public class NestedIOException extends IOException {
 	 * if there is one.
 	 */
 	@Override
+	@Nullable
 	public String getMessage() {
 		return NestedExceptionUtils.buildMessage(super.getMessage(), getCause());
 	}

spring-core/src/main/java/org/springframework/core/NestedRuntimeException.java

@@ -62,7 +62,7 @@ public abstract class NestedRuntimeException extends RuntimeException {
 	 * @param msg the detail message
 	 * @param cause the nested exception
 	 */
-	public NestedRuntimeException(String msg, Throwable cause) {
+	public NestedRuntimeException(@Nullable String msg, @Nullable Throwable cause) {
 		super(msg, cause);
 	}
 
@@ -72,6 +72,7 @@ public abstract class NestedRuntimeException extends RuntimeException {
 	 * if there is one.
 	 */
 	@Override
+	@Nullable
 	public String getMessage() {
 		return NestedExceptionUtils.buildMessage(super.getMessage(), getCause());
 	}
@@ -107,7 +108,7 @@ public abstract class NestedRuntimeException extends RuntimeException {
 	 * @param exType the exception type to look for
 	 * @return whether there is a nested exception of the specified type
 	 */
-	public boolean contains(Class<?> exType) {
+	public boolean contains(@Nullable Class<?> exType) {
 		if (exType == null) {
 			return false;
 		}

spring-core/src/main/java/org/springframework/core/OrderComparator.java

@@ -61,12 +61,7 @@ public class OrderComparator implements Comparator<Object> {
 	 * @since 4.1
 	 */
 	public Comparator<Object> withSourceProvider(final OrderSourceProvider sourceProvider) {
-		return new Comparator<Object>() {
-			@Override
-			public int compare(Object o1, Object o2) {
-				return doCompare(o1, o2, sourceProvider);
-			}
-		};
+		return (o1, o2) -> doCompare(o1, o2, sourceProvider);
 	}
 
 	@Override
@@ -97,21 +92,23 @@ public class OrderComparator implements Comparator<Object> {
 	 * @param obj the object to check
 	 * @return the order value, or {@code Ordered.LOWEST_PRECEDENCE} as fallback
 	 */
-	private int getOrder(Object obj, OrderSourceProvider sourceProvider) {
+	private int getOrder(Object obj, @Nullable OrderSourceProvider sourceProvider) {
 		Integer order = null;
 		if (sourceProvider != null) {
 			Object orderSource = sourceProvider.getOrderSource(obj);
-			if (orderSource != null && orderSource.getClass().isArray()) {
-				Object[] sources = ObjectUtils.toObjectArray(orderSource);
-				for (Object source : sources) {
-					order = findOrder(source);
-					if (order != null) {
-						break;
+			if (orderSource != null) {
+				if (orderSource.getClass().isArray()) {
+					Object[] sources = ObjectUtils.toObjectArray(orderSource);
+					for (Object source : sources) {
+						order = findOrder(source);
+						if (order != null) {
+							break;
+						}
 					}
 				}
-			}
-			else {
-				order = findOrder(orderSource);
+				else {
+					order = findOrder(orderSource);
+				}
 			}
 		}
 		return (order != null ? order : getOrder(obj));

spring-core/src/main/java/org/springframework/core/OverridingClassLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -54,7 +54,7 @@ public class OverridingClassLoader extends DecoratingClassLoader {
 	 * Create a new OverridingClassLoader for the given ClassLoader.
 	 * @param parent the ClassLoader to build an overriding ClassLoader for
 	 */
-	public OverridingClassLoader(ClassLoader parent) {
+	public OverridingClassLoader(@Nullable ClassLoader parent) {
 		this(parent, null);
 	}
 
@@ -64,7 +64,7 @@ public class OverridingClassLoader extends DecoratingClassLoader {
 	 * @param overrideDelegate the ClassLoader to delegate to for overriding
 	 * @since 4.3
 	 */
-	public OverridingClassLoader(ClassLoader parent, ClassLoader overrideDelegate) {
+	public OverridingClassLoader(@Nullable ClassLoader parent, @Nullable ClassLoader overrideDelegate) {
 		super(parent);
 		this.overrideDelegate = overrideDelegate;
 		for (String packageName : DEFAULT_EXCLUDED_PACKAGES) {
@@ -160,6 +160,7 @@ public class OverridingClassLoader extends DecoratingClassLoader {
 	 * @param name the name of the class
 	 * @return the InputStream containing the byte code for the specified class
 	 */
+	@Nullable
 	protected InputStream openStreamForClass(String name) {
 		String internalName = name.replace('.', '/') + CLASS_FILE_SUFFIX;
 		return getParent().getResourceAsStream(internalName);

spring-core/src/main/java/org/springframework/core/ReactiveAdapter.java

@@ -20,6 +20,7 @@ import java.util.function.Function;
 
 import org.reactivestreams.Publisher;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -104,7 +105,7 @@ public class ReactiveAdapter {
 	 * @return the Publisher representing the adaptation
 	 */
 	@SuppressWarnings("unchecked")
-	public <T> Publisher<T> toPublisher(Object source) {
+	public <T> Publisher<T> toPublisher(@Nullable Object source) {
 		if (source == null) {
 			source = getDescriptor().getEmptyValue();
 		}
@@ -117,7 +118,7 @@ public class ReactiveAdapter {
 	 * @return the reactive type instance representing the adapted publisher
 	 */
 	public Object fromPublisher(Publisher<?> publisher) {
-		return (publisher != null ? this.fromPublisherFunction.apply(publisher) : null);
+		return this.fromPublisherFunction.apply(publisher);
 	}
 
 }

spring-core/src/main/java/org/springframework/core/ReactiveAdapterRegistry.java

@@ -109,7 +109,8 @@ public class ReactiveAdapterRegistry {
 	/**
 	 * Get the adapter for the given reactive type.
 	 */
-	public ReactiveAdapter getAdapter(@Nullable Class<?> reactiveType) {
+	@Nullable
+	public ReactiveAdapter getAdapter(Class<?> reactiveType) {
 		return getAdapter(reactiveType, null);
 	}
 
@@ -123,7 +124,6 @@ public class ReactiveAdapterRegistry {
 	 */
 	@Nullable
 	public ReactiveAdapter getAdapter(@Nullable Class<?> reactiveType, @Nullable Object source) {
-
 		Object sourceToUse = (source instanceof Optional ? ((Optional<?>) source).orElse(null) : source);
 		Class<?> clazz = (sourceToUse != null ? sourceToUse.getClass() : reactiveType);
 		if (clazz == null) {

spring-core/src/main/java/org/springframework/core/ReactiveTypeDescriptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -13,6 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 package org.springframework.core;
 
 import java.util.function.Supplier;
@@ -99,7 +100,7 @@ public class ReactiveTypeDescriptor {
 
 
 	@Override
-	public boolean equals(Object other) {
+	public boolean equals(@Nullable Object other) {
 		if (this == other) {
 			return true;
 		}

spring-core/src/main/java/org/springframework/core/ResolvableType.java

@@ -132,7 +132,7 @@ public class ResolvableType implements Serializable {
 	 * Private constructor used to create a new {@link ResolvableType} for cache key purposes,
 	 * with no upfront resolution.
 	 */
-	private ResolvableType(Type type, TypeProvider typeProvider, VariableResolver variableResolver) {
+	private ResolvableType(Type type, @Nullable TypeProvider typeProvider, @Nullable VariableResolver variableResolver) {
 		this.type = type;
 		this.typeProvider = typeProvider;
 		this.variableResolver = variableResolver;
@@ -146,7 +146,9 @@ public class ResolvableType implements Serializable {
 	 * with upfront resolution and a pre-calculated hash.
 	 * @since 4.2
 	 */
-	private ResolvableType(@Nullable Type type, @Nullable TypeProvider typeProvider, @Nullable VariableResolver variableResolver, Integer hash) {
+	private ResolvableType(@Nullable Type type, @Nullable TypeProvider typeProvider,
+			@Nullable VariableResolver variableResolver, Integer hash) {
+
 		this.type = type;
 		this.typeProvider = typeProvider;
 		this.variableResolver = variableResolver;
@@ -159,8 +161,8 @@ public class ResolvableType implements Serializable {
 	 * Private constructor used to create a new {@link ResolvableType} for uncached purposes,
 	 * with upfront resolution but lazily calculated hash.
 	 */
-	private ResolvableType(
-			Type type, @Nullable TypeProvider typeProvider, @Nullable VariableResolver variableResolver, ResolvableType componentType) {
+	private ResolvableType(Type type, @Nullable TypeProvider typeProvider,
+			@Nullable VariableResolver variableResolver, @Nullable ResolvableType componentType) {
 
 		this.type = type;
 		this.typeProvider = typeProvider;
@@ -175,7 +177,7 @@ public class ResolvableType implements Serializable {
 	 * Avoids all {@code instanceof} checks in order to create a straight {@link Class} wrapper.
 	 * @since 4.2
 	 */
-	private ResolvableType(Class<?> clazz) {
+	private ResolvableType(@Nullable Class<?> clazz) {
 		this.resolved = (clazz != null ? clazz : Object.class);
 		this.type = this.resolved;
 		this.typeProvider = null;
@@ -189,6 +191,7 @@ public class ResolvableType implements Serializable {
 	 * Return the underling Java {@link Type} being managed. With the exception of
 	 * the {@link #NONE} constant, this method will never return {@code null}.
 	 */
+	@Nullable
 	public Type getType() {
 		return SerializableTypeWrapper.unwrap(this.type);
 	}
@@ -227,7 +230,7 @@ public class ResolvableType implements Serializable {
 	 * @since 4.2
 	 * @see #isAssignableFrom(Class)
 	 */
-	public boolean isInstance(Object obj) {
+	public boolean isInstance(@Nullable Object obj) {
 		return (obj != null && isAssignableFrom(obj.getClass()));
 	}
 
@@ -625,7 +628,7 @@ public class ResolvableType implements Serializable {
 	 * @see #resolveGeneric(int...)
 	 * @see #resolveGenerics()
 	 */
-	public ResolvableType getGeneric(int... indexes) {
+	public ResolvableType getGeneric(@Nullable int... indexes) {
 		ResolvableType[] generics = getGenerics();
 		if (indexes == null || indexes.length == 0) {
 			return (generics.length == 0 ? NONE : generics[0]);
@@ -687,20 +690,24 @@ public class ResolvableType implements Serializable {
 	 * @see #resolve()
 	 */
 	public Class<?>[] resolveGenerics() {
-		return resolveGenerics(null);
+		ResolvableType[] generics = getGenerics();
+		Class<?>[] resolvedGenerics = new Class<?>[generics.length];
+		for (int i = 0; i < generics.length; i++) {
+			resolvedGenerics[i] = generics[i].resolve();
+		}
+		return resolvedGenerics;
 	}
 
 	/**
 	 * Convenience method that will {@link #getGenerics() get} and {@link #resolve()
 	 * resolve} generic parameters, using the specified {@code fallback} if any type
 	 * cannot be resolved.
-	 * @param fallback the fallback class to use if resolution fails (may be {@code null})
-	 * @return an array of resolved generic parameters (the resulting array will never be
-	 * {@code null}, but it may contain {@code null} elements})
+	 * @param fallback the fallback class to use if resolution fails
+	 * @return an array of resolved generic parameters
 	 * @see #getGenerics()
 	 * @see #resolve()
 	 */
-	public Class<?>[] resolveGenerics(@Nullable Class<?> fallback) {
+	public Class<?>[] resolveGenerics(Class<?> fallback) {
 		ResolvableType[] generics = getGenerics();
 		Class<?>[] resolvedGenerics = new Class<?>[generics.length];
 		for (int i = 0; i < generics.length; i++) {
@@ -735,7 +742,7 @@ public class ResolvableType implements Serializable {
 	 */
 	@Nullable
 	public Class<?> resolve() {
-		return resolve(null);
+		return (this.resolved != null ? this.resolved : null);
 	}
 
 	/**
@@ -743,13 +750,13 @@ public class ResolvableType implements Serializable {
 	 * {@code fallback} if the type cannot be resolved. This method will consider bounds
 	 * of {@link TypeVariable}s and {@link WildcardType}s if direct resolution fails;
 	 * however, bounds of {@code Object.class} will be ignored.
-	 * @param fallback the fallback class to use if resolution fails (may be {@code null})
+	 * @param fallback the fallback class to use if resolution fails
 	 * @return the resolved {@link Class} or the {@code fallback}
 	 * @see #resolve()
 	 * @see #resolveGeneric(int...)
 	 * @see #resolveGenerics()
 	 */
-	public Class<?> resolve(@Nullable Class<?> fallback) {
+	public Class<?> resolve(Class<?> fallback) {
 		return (this.resolved != null ? this.resolved : fallback);
 	}
 
@@ -810,15 +817,20 @@ public class ResolvableType implements Serializable {
 		}
 		if (this.type instanceof ParameterizedType) {
 			ParameterizedType parameterizedType = (ParameterizedType) this.type;
-			TypeVariable<?>[] variables = resolve().getTypeParameters();
+			Class<?> resolved = resolve();
+			if (resolved == null) {
+				return null;
+			}
+			TypeVariable<?>[] variables = resolved.getTypeParameters();
 			for (int i = 0; i < variables.length; i++) {
 				if (ObjectUtils.nullSafeEquals(variables[i].getName(), variable.getName())) {
 					Type actualType = parameterizedType.getActualTypeArguments()[i];
 					return forType(actualType, this.variableResolver);
 				}
 			}
-			if (parameterizedType.getOwnerType() != null) {
-				return forType(parameterizedType.getOwnerType(), this.variableResolver).resolveVariable(variable);
+			Type ownerType = parameterizedType.getOwnerType();
+			if (ownerType != null) {
+				return forType(ownerType, this.variableResolver).resolveVariable(variable);
 			}
 		}
 		if (this.variableResolver != null) {
@@ -960,12 +972,12 @@ public class ResolvableType implements Serializable {
 			}
 			@Override
 			public boolean isAssignableFrom(Class<?> other) {
-				return ClassUtils.isAssignable(getRawClass(), other);
+				return (clazz == null || ClassUtils.isAssignable(clazz, other));
 			}
 			@Override
 			public boolean isAssignableFrom(ResolvableType other) {
 				Class<?> otherClass = other.getRawClass();
-				return (otherClass != null && ClassUtils.isAssignable(getRawClass(), otherClass));
+				return (otherClass != null && (clazz == null || ClassUtils.isAssignable(clazz, otherClass)));
 			}
 		};
 	}
@@ -1086,7 +1098,7 @@ public class ResolvableType implements Serializable {
 	 * @return a {@link ResolvableType} for the specified field
 	 * @see #forField(Field)
 	 */
-	public static ResolvableType forField(Field field, ResolvableType implementationType) {
+	public static ResolvableType forField(Field field, @Nullable ResolvableType implementationType) {
 		Assert.notNull(field, "Field must not be null");
 		ResolvableType owner = (implementationType != null ? implementationType : NONE);
 		owner = owner.as(field.getDeclaringClass());
@@ -1233,7 +1245,9 @@ public class ResolvableType implements Serializable {
 	 * @return a {@link ResolvableType} for the specified method parameter
 	 * @see #forMethodParameter(MethodParameter)
 	 */
-	public static ResolvableType forMethodParameter(MethodParameter methodParameter, ResolvableType implementationType) {
+	public static ResolvableType forMethodParameter(MethodParameter methodParameter,
+			@Nullable ResolvableType implementationType) {
+
 		Assert.notNull(methodParameter, "MethodParameter must not be null");
 		implementationType = (implementationType != null ? implementationType :
 				forType(methodParameter.getContainingClass()));
@@ -1250,7 +1264,7 @@ public class ResolvableType implements Serializable {
 	 * @return a {@link ResolvableType} for the specified method parameter
 	 * @see #forMethodParameter(Method, int)
 	 */
-	public static ResolvableType forMethodParameter(MethodParameter methodParameter, Type targetType) {
+	public static ResolvableType forMethodParameter(MethodParameter methodParameter, @Nullable Type targetType) {
 		Assert.notNull(methodParameter, "MethodParameter must not be null");
 		ResolvableType owner = forType(methodParameter.getContainingClass()).as(methodParameter.getDeclaringClass());
 		return forType(targetType, new MethodParameterTypeProvider(methodParameter), owner.asVariableResolver()).
@@ -1281,7 +1295,7 @@ public class ResolvableType implements Serializable {
 		return new ResolvableType(arrayClass, null, null, componentType);
 	}
 
-	private static ResolvableType[] forTypes(Type[] types, VariableResolver owner) {
+	private static ResolvableType[] forTypes(Type[] types, @Nullable VariableResolver owner) {
 		ResolvableType[] result = new ResolvableType[types.length];
 		for (int i = 0; i < types.length; i++) {
 			result[i] = forType(types[i], owner);
@@ -1292,7 +1306,7 @@ public class ResolvableType implements Serializable {
 	/**
 	 * Return a {@link ResolvableType} for the specified {@link Type}.
 	 * Note: The resulting {@link ResolvableType} may not be {@link Serializable}.
-	 * @param type the source type or {@code null}
+	 * @param type the source type (potentially {@code null})
 	 * @return a {@link ResolvableType} for the specified {@link Type}
 	 * @see #forType(Type, ResolvableType)
 	 */
@@ -1308,7 +1322,7 @@ public class ResolvableType implements Serializable {
 	 * @return a {@link ResolvableType} for the specified {@link Type} and owner
 	 * @see #forType(Type)
 	 */
-	public static ResolvableType forType(@Nullable Type type, ResolvableType owner) {
+	public static ResolvableType forType(@Nullable Type type, @Nullable ResolvableType owner) {
 		VariableResolver variableResolver = null;
 		if (owner != null) {
 			variableResolver = owner.asVariableResolver();
@@ -1422,7 +1436,7 @@ public class ResolvableType implements Serializable {
 		@Override
 		public ResolvableType resolveVariable(TypeVariable<?> variable) {
 			for (int i = 0; i < this.variables.length; i++) {
-				if (SerializableTypeWrapper.unwrap(this.variables[i]).equals(
+				if (ObjectUtils.nullSafeEquals(SerializableTypeWrapper.unwrap(this.variables[i]),
 						SerializableTypeWrapper.unwrap(variable))) {
 					return this.generics[i];
 				}
@@ -1553,6 +1567,7 @@ public class ResolvableType implements Serializable {
 				resolveToWildcard = resolveToWildcard.resolveType();
 			}
 			WildcardType wildcardType = (WildcardType) resolveToWildcard.type;
+			Assert.state(wildcardType != null, "Wildcard type not resolved");
 			Kind boundsType = (wildcardType.getLowerBounds().length > 0 ? Kind.LOWER : Kind.UPPER);
 			Type[] bounds = boundsType == Kind.UPPER ? wildcardType.getUpperBounds() : wildcardType.getLowerBounds();
 			ResolvableType[] resolvableBounds = new ResolvableType[bounds.length];

spring-core/src/main/java/org/springframework/core/ResolvableTypeProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,7 +26,7 @@ import org.springframework.lang.Nullable;
  *
  * <p>Users of this interface should be careful in complex hierarchy scenarios, especially
  * when the generic type signature of the class changes in sub-classes. It is always
- * possible to return {@code null} to fallback on a default behaviour.
+ * possible to return {@code null} to fallback on a default behavior.
  *
  * @author Stephane Nicoll
  * @since 4.2

spring-core/src/main/java/org/springframework/core/SerializableTypeWrapper.java

@@ -33,6 +33,7 @@ import java.lang.reflect.WildcardType;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ConcurrentReferenceHashMap;
+import org.springframework.util.ObjectUtils;
 import org.springframework.util.ReflectionUtils;
 
 /**
@@ -66,6 +67,7 @@ abstract class SerializableTypeWrapper {
 	/**
 	 * Return a {@link Serializable} variant of {@link Field#getGenericType()}.
 	 */
+	@Nullable
 	public static Type forField(Field field) {
 		Assert.notNull(field, "Field must not be null");
 		return forTypeProvider(new FieldTypeProvider(field));
@@ -75,6 +77,7 @@ abstract class SerializableTypeWrapper {
 	 * Return a {@link Serializable} variant of
 	 * {@link MethodParameter#getGenericParameterType()}.
 	 */
+	@Nullable
 	public static Type forMethodParameter(MethodParameter methodParameter) {
 		return forTypeProvider(new MethodParameterTypeProvider(methodParameter));
 	}
@@ -83,6 +86,7 @@ abstract class SerializableTypeWrapper {
 	 * Return a {@link Serializable} variant of {@link Class#getGenericSuperclass()}.
 	 */
 	@SuppressWarnings("serial")
+	@Nullable
 	public static Type forGenericSuperclass(final Class<?> type) {
 		return forTypeProvider(type::getGenericSuperclass);
 	}
@@ -119,6 +123,7 @@ abstract class SerializableTypeWrapper {
 	 * @return the original non-serializable type
 	 */
 	@SuppressWarnings("unchecked")
+	@Nullable
 	public static <T extends Type> T unwrap(T type) {
 		Type unwrapped = type;
 		while (unwrapped instanceof SerializableTypeProxy) {
@@ -130,26 +135,31 @@ abstract class SerializableTypeWrapper {
 	/**
 	 * Return a {@link Serializable} {@link Type} backed by a {@link TypeProvider} .
 	 */
+	@Nullable
 	static Type forTypeProvider(final TypeProvider provider) {
 		Assert.notNull(provider, "Provider must not be null");
-		if (provider.getType() instanceof Serializable || provider.getType() == null) {
-			return provider.getType();
+		Type providedType = provider.getType();
+		if (providedType == null) {
+			return null;
 		}
-		Type cached = cache.get(provider.getType());
+		if (providedType instanceof Serializable) {
+			return providedType;
+		}
+		Type cached = cache.get(providedType);
 		if (cached != null) {
 			return cached;
 		}
 		for (Class<?> type : SUPPORTED_SERIALIZABLE_TYPES) {
-			if (type.isAssignableFrom(provider.getType().getClass())) {
+			if (type.isAssignableFrom(providedType.getClass())) {
 				ClassLoader classLoader = provider.getClass().getClassLoader();
 				Class<?>[] interfaces = new Class<?>[] {type, SerializableTypeProxy.class, Serializable.class};
 				InvocationHandler handler = new TypeProxyInvocationHandler(provider);
 				cached = (Type) Proxy.newProxyInstance(classLoader, interfaces, handler);
-				cache.put(provider.getType(), cached);
+				cache.put(providedType, cached);
 				return cached;
 			}
 		}
-		throw new IllegalArgumentException("Unsupported Type class: " + provider.getType().getClass().getName());
+		throw new IllegalArgumentException("Unsupported Type class: " + providedType.getClass().getName());
 	}
 
 
@@ -174,6 +184,7 @@ abstract class SerializableTypeWrapper {
 		/**
 		 * Return the (possibly non {@link Serializable}) {@link Type}.
 		 */
+		@Nullable
 		Type getType();
 
 		/**
@@ -202,17 +213,18 @@ abstract class SerializableTypeWrapper {
 		}
 
 		@Override
-		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
-			if (method.getName().equals("equals")) {
+		@Nullable
+		public Object invoke(Object proxy, Method method, @Nullable Object[] args) throws Throwable {
+			if (method.getName().equals("equals") && args != null) {
 				Object other = args[0];
 				// Unwrap proxies for speed
 				if (other instanceof Type) {
 					other = unwrap((Type) other);
 				}
-				return this.provider.getType().equals(other);
+				return ObjectUtils.nullSafeEquals(this.provider.getType(), other);
 			}
 			else if (method.getName().equals("hashCode")) {
-				return this.provider.getType().hashCode();
+				return ObjectUtils.nullSafeHashCode(this.provider.getType());
 			}
 			else if (method.getName().equals("getTypeProvider")) {
 				return this.provider;
@@ -222,7 +234,7 @@ abstract class SerializableTypeWrapper {
 				return forTypeProvider(new MethodInvokeTypeProvider(this.provider, method, -1));
 			}
 			else if (Type[].class == method.getReturnType() && args == null) {
-				Type[] result = new Type[((Type[]) method.invoke(this.provider.getType(), args)).length];
+				Type[] result = new Type[((Type[]) method.invoke(this.provider.getType())).length];
 				for (int i = 0; i < result.length; i++) {
 					result[i] = forTypeProvider(new MethodInvokeTypeProvider(this.provider, method, i));
 				}
@@ -296,20 +308,13 @@ abstract class SerializableTypeWrapper {
 		private transient MethodParameter methodParameter;
 
 		public MethodParameterTypeProvider(MethodParameter methodParameter) {
-			if (methodParameter.getMethod() != null) {
-				this.methodName = methodParameter.getMethod().getName();
-				this.parameterTypes = methodParameter.getMethod().getParameterTypes();
-			}
-			else {
-				this.methodName = null;
-				this.parameterTypes = methodParameter.getConstructor().getParameterTypes();
-			}
+			this.methodName = (methodParameter.getMethod() != null ? methodParameter.getMethod().getName() : null);
+			this.parameterTypes = methodParameter.getExecutable().getParameterTypes();
 			this.declaringClass = methodParameter.getDeclaringClass();
 			this.parameterIndex = methodParameter.getParameterIndex();
 			this.methodParameter = methodParameter;
 		}
 
-
 		@Override
 		public Type getType() {
 			return this.methodParameter.getGenericParameterType();
@@ -385,6 +390,9 @@ abstract class SerializableTypeWrapper {
 		private void readObject(ObjectInputStream inputStream) throws IOException, ClassNotFoundException {
 			inputStream.defaultReadObject();
 			this.method = ReflectionUtils.findMethod(this.declaringClass, this.methodName);
+			if (this.method == null) {
+				throw new IllegalStateException("Cannot find method on deserialization: " + this.methodName);
+			}
 			if (this.method.getReturnType() != Type.class && this.method.getReturnType() != Type[].class) {
 				throw new IllegalStateException(
 						"Invalid return type on deserialized method - needs to be Type or Type[]: " + this.method);

spring-core/src/main/java/org/springframework/core/annotation/AbstractAliasAwareAnnotationAttributeExtractor.java

@@ -121,6 +121,7 @@ abstract class AbstractAliasAwareAnnotationAttributeExtractor<S> implements Anno
 	 * {@linkplain #getSource source} that corresponds to the supplied
 	 * attribute method.
 	 */
+	@Nullable
 	protected abstract Object getRawAttributeValue(Method attributeMethod);
 
 	/**
@@ -128,6 +129,7 @@ abstract class AbstractAliasAwareAnnotationAttributeExtractor<S> implements Anno
 	 * {@linkplain #getSource source} that corresponds to the supplied
 	 * attribute name.
 	 */
+	@Nullable
 	protected abstract Object getRawAttributeValue(String attributeName);
 
 }

spring-core/src/main/java/org/springframework/core/annotation/AnnotatedElementUtils.java

@@ -21,6 +21,7 @@ import java.lang.reflect.AnnotatedElement;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -117,6 +118,7 @@ public class AnnotatedElementUtils {
 		return new AnnotatedElement() {
 			@Override
 			@SuppressWarnings("unchecked")
+			@Nullable
 			public <T extends Annotation> T getAnnotation(Class<T> annotationClass) {
 				for (Annotation ann : annotations) {
 					if (ann.annotationType() == annotationClass) {
@@ -168,11 +170,10 @@ public class AnnotatedElementUtils {
 	 * @param annotationName the fully qualified class name of the annotation
 	 * type on which to find meta-annotations
 	 * @return the names of all meta-annotations present on the annotation,
-	 * or {@code null} if not found
+	 * or an empty set if none found
 	 * @see #getMetaAnnotationTypes(AnnotatedElement, Class)
 	 * @see #hasMetaAnnotationTypes
 	 */
-	@Nullable
 	public static Set<String> getMetaAnnotationTypes(AnnotatedElement element, String annotationName) {
 		Assert.notNull(element, "AnnotatedElement must not be null");
 		Assert.hasLength(annotationName, "'annotationName' must not be null or empty");
@@ -180,9 +181,9 @@ public class AnnotatedElementUtils {
 		return getMetaAnnotationTypes(element, AnnotationUtils.getAnnotation(element, annotationName));
 	}
 
-	private static Set<String> getMetaAnnotationTypes(AnnotatedElement element, Annotation composed) {
+	private static Set<String> getMetaAnnotationTypes(AnnotatedElement element, @Nullable Annotation composed) {
 		if (composed == null) {
-			return null;
+			return Collections.emptySet();
 		}
 
 		try {
@@ -195,7 +196,7 @@ public class AnnotatedElementUtils {
 						return CONTINUE;
 					}
 				}, new HashSet<>(), 1);
-			return (!types.isEmpty() ? types : null);
+			return types;
 		}
 		catch (Throwable ex) {
 			AnnotationUtils.rethrowAnnotationConfigurationException(ex);
@@ -844,7 +845,8 @@ public class AnnotatedElementUtils {
 	 * @return the result of the processor, potentially {@code null}
 	 */
 	@Nullable
-	private static <T> T searchWithGetSemantics(AnnotatedElement element, @Nullable Class<? extends Annotation> annotationType,
+	private static <T> T searchWithGetSemantics(AnnotatedElement element,
+			@Nullable Class<? extends Annotation> annotationType,
 			@Nullable String annotationName, Processor<T> processor) {
 
 		return searchWithGetSemantics(element, annotationType, annotationName, null, processor);
@@ -865,8 +867,9 @@ public class AnnotatedElementUtils {
 	 * @since 4.3
 	 */
 	@Nullable
-	private static <T> T searchWithGetSemantics(AnnotatedElement element, Class<? extends Annotation> annotationType,
-			@Nullable String annotationName, @Nullable Class<? extends Annotation> containerType, Processor<T> processor) {
+	private static <T> T searchWithGetSemantics(AnnotatedElement element,
+			@Nullable Class<? extends Annotation> annotationType, @Nullable String annotationName,
+			@Nullable Class<? extends Annotation> containerType, Processor<T> processor) {
 
 		try {
 			return searchWithGetSemantics(element, annotationType, annotationName, containerType, processor,
@@ -896,8 +899,9 @@ public class AnnotatedElementUtils {
 	 * @return the result of the processor, potentially {@code null}
 	 */
 	@Nullable
-	private static <T> T searchWithGetSemantics(AnnotatedElement element, @Nullable Class<? extends Annotation> annotationType,
-			@Nullable String annotationName, @Nullable Class<? extends Annotation> containerType, Processor<T> processor,
+	private static <T> T searchWithGetSemantics(AnnotatedElement element,
+			@Nullable Class<? extends Annotation> annotationType, @Nullable String annotationName,
+			@Nullable Class<? extends Annotation> containerType, Processor<T> processor,
 			Set<AnnotatedElement> visited, int metaDepth) {
 
 		Assert.notNull(element, "AnnotatedElement must not be null");
@@ -960,9 +964,9 @@ public class AnnotatedElementUtils {
 	 */
 	@Nullable
 	private static <T> T searchWithGetSemanticsInAnnotations(@Nullable AnnotatedElement element,
-			List<Annotation> annotations, Class<? extends Annotation> annotationType, String annotationName,
-			@Nullable Class<? extends Annotation> containerType, Processor<T> processor, Set<AnnotatedElement> visited,
-			int metaDepth) {
+			List<Annotation> annotations, @Nullable Class<? extends Annotation> annotationType,
+			@Nullable String annotationName, @Nullable Class<? extends Annotation> containerType,
+			Processor<T> processor, Set<AnnotatedElement> visited, int metaDepth) {
 
 		// Search in annotations
 		for (Annotation annotation : annotations) {
@@ -1029,7 +1033,8 @@ public class AnnotatedElementUtils {
 	 * @since 4.2
 	 */
 	@Nullable
-	private static <T> T searchWithFindSemantics(AnnotatedElement element, @Nullable Class<? extends Annotation> annotationType,
+	private static <T> T searchWithFindSemantics(AnnotatedElement element,
+			@Nullable Class<? extends Annotation> annotationType,
 			@Nullable String annotationName, Processor<T> processor) {
 
 		return searchWithFindSemantics(element, annotationType, annotationName, null, processor);
@@ -1050,8 +1055,9 @@ public class AnnotatedElementUtils {
 	 * @since 4.3
 	 */
 	@Nullable
-	private static <T> T searchWithFindSemantics(AnnotatedElement element, Class<? extends Annotation> annotationType,
-			@Nullable String annotationName, @Nullable Class<? extends Annotation> containerType, Processor<T> processor) {
+	private static <T> T searchWithFindSemantics(AnnotatedElement element,
+			@Nullable Class<? extends Annotation> annotationType, @Nullable String annotationName,
+			@Nullable Class<? extends Annotation> containerType, Processor<T> processor) {
 
 		if (containerType != null && !processor.aggregates()) {
 			throw new IllegalArgumentException(
@@ -1087,8 +1093,9 @@ public class AnnotatedElementUtils {
 	 * @since 4.2
 	 */
 	@Nullable
-	private static <T> T searchWithFindSemantics(AnnotatedElement element, Class<? extends Annotation> annotationType,
-			String annotationName, @Nullable Class<? extends Annotation> containerType, Processor<T> processor,
+	private static <T> T searchWithFindSemantics(AnnotatedElement element,
+			@Nullable Class<? extends Annotation> annotationType, @Nullable String annotationName,
+			@Nullable Class<? extends Annotation> containerType, Processor<T> processor,
 			Set<AnnotatedElement> visited, int metaDepth) {
 
 		Assert.notNull(element, "AnnotatedElement must not be null");
@@ -1260,11 +1267,14 @@ public class AnnotatedElementUtils {
 	 * @since 4.3
 	 */
 	@SuppressWarnings("unchecked")
-	private static <A extends Annotation> A[] getRawAnnotationsFromContainer(AnnotatedElement element,
-			Annotation container) {
+	private static <A extends Annotation> A[] getRawAnnotationsFromContainer(
+			@Nullable AnnotatedElement element, Annotation container) {
 
 		try {
-			return (A[]) AnnotationUtils.getValue(container);
+			A[] value = (A[]) AnnotationUtils.getValue(container);
+			if (value != null) {
+				return value;
+			}
 		}
 		catch (Throwable ex) {
 			AnnotationUtils.handleIntrospectionFailure(element, ex);
@@ -1597,7 +1607,7 @@ public class AnnotatedElementUtils {
 			}
 		}
 
-		private void overrideAttributes(AnnotatedElement element, Annotation annotation,
+		private void overrideAttributes(@Nullable AnnotatedElement element, Annotation annotation,
 				AnnotationAttributes attributes, String sourceAttributeName, List<String> targetAttributeNames) {
 
 			Object adaptedValue = getAdaptedValue(element, annotation, sourceAttributeName);
@@ -1607,13 +1617,16 @@ public class AnnotatedElementUtils {
 			}
 		}
 
-		private void overrideAttribute(AnnotatedElement element, Annotation annotation, AnnotationAttributes attributes,
-				String sourceAttributeName, String targetAttributeName) {
+		private void overrideAttribute(@Nullable AnnotatedElement element, Annotation annotation,
+				AnnotationAttributes attributes, String sourceAttributeName, String targetAttributeName) {
 
 			attributes.put(targetAttributeName, getAdaptedValue(element, annotation, sourceAttributeName));
 		}
 
-		private Object getAdaptedValue(AnnotatedElement element, Annotation annotation, String sourceAttributeName) {
+		@Nullable
+		private Object getAdaptedValue(
+				@Nullable AnnotatedElement element, Annotation annotation, String sourceAttributeName) {
+
 			Object value = AnnotationUtils.getValue(annotation, sourceAttributeName);
 			return AnnotationUtils.adaptValue(element, value, this.classValuesAsString, this.nestedAnnotationsAsMap);
 		}

spring-core/src/main/java/org/springframework/core/annotation/AnnotationAttributeExtractor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -60,6 +60,7 @@ interface AnnotationAttributeExtractor<S> {
 	 * supported by this extractor
 	 * @return the value of the annotation attribute
 	 */
+	@Nullable
 	Object getAttributeValue(Method attributeMethod);
 
 }

spring-core/src/main/java/org/springframework/core/annotation/AnnotationAttributes.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,7 +50,7 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 
 	private final Class<? extends Annotation> annotationType;
 
-	private final String displayName;
+	final String displayName;
 
 	boolean validated = false;
 
@@ -128,7 +128,8 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	}
 
 	@SuppressWarnings("unchecked")
-	private static Class<? extends Annotation> getAnnotationType(String annotationType, ClassLoader classLoader) {
+	@Nullable
+	private static Class<? extends Annotation> getAnnotationType(String annotationType, @Nullable ClassLoader classLoader) {
 		if (classLoader != null) {
 			try {
 				return (Class<? extends Annotation>) classLoader.loadClass(annotationType);
@@ -142,8 +143,7 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 
 
 	/**
-	 * Get the type of annotation represented by this
-	 * {@code AnnotationAttributes} instance.
+	 * Get the type of annotation represented by this {@code AnnotationAttributes}.
 	 * @return the annotation type, or {@code null} if unknown
 	 * @since 4.2
 	 */
@@ -153,10 +153,9 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	}
 
 	/**
-	 * Get the value stored under the specified {@code attributeName} as a
-	 * string.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * Get the value stored under the specified {@code attributeName} as a string.
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @return the value
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
@@ -171,8 +170,8 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	 * <p>If the value stored under the specified {@code attributeName} is
 	 * a string, it will be wrapped in a single-element array before
 	 * returning it.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @return the value
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
@@ -182,10 +181,9 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	}
 
 	/**
-	 * Get the value stored under the specified {@code attributeName} as a
-	 * boolean.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * Get the value stored under the specified {@code attributeName} as a boolean.
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @return the value
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
@@ -195,10 +193,9 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	}
 
 	/**
-	 * Get the value stored under the specified {@code attributeName} as a
-	 * number.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * Get the value stored under the specified {@code attributeName} as a number.
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @return the value
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
@@ -209,10 +206,9 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	}
 
 	/**
-	 * Get the value stored under the specified {@code attributeName} as an
-	 * enum.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * Get the value stored under the specified {@code attributeName} as an enum.
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @return the value
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
@@ -223,10 +219,9 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	}
 
 	/**
-	 * Get the value stored under the specified {@code attributeName} as a
-	 * class.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * Get the value stored under the specified {@code attributeName} as a class.
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @return the value
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
@@ -239,11 +234,10 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	/**
 	 * Get the value stored under the specified {@code attributeName} as an
 	 * array of classes.
-	 * <p>If the value stored under the specified {@code attributeName} is
-	 * a class, it will be wrapped in a single-element array before
-	 * returning it.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * <p>If the value stored under the specified {@code attributeName} is a class,
+	 * it will be wrapped in a single-element array before returning it.
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @return the value
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
@@ -257,8 +251,8 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	 * {@code attributeName}.
 	 * <p>Note: if you expect an actual annotation, invoke
 	 * {@link #getAnnotation(String, Class)} instead.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @return the {@code AnnotationAttributes}
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
@@ -270,8 +264,8 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	/**
 	 * Get the annotation of type {@code annotationType} stored under the
 	 * specified {@code attributeName}.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @param annotationType the expected annotation type; never {@code null}
 	 * @return the annotation
 	 * @throws IllegalArgumentException if the attribute does not exist or
@@ -290,8 +284,8 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	 * a single-element array before returning it.
 	 * <p>Note: if you expect an actual array of annotations, invoke
 	 * {@link #getAnnotationArray(String, Class)} instead.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @return the array of {@code AnnotationAttributes}
 	 * @throws IllegalArgumentException if the attribute does not exist or
 	 * if it is not of the expected type
@@ -306,8 +300,8 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	 * <p>If the value stored under the specified {@code attributeName} is
 	 * an {@code Annotation}, it will be wrapped in a single-element array
 	 * before returning it.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @param annotationType the expected annotation type; never {@code null}
 	 * @return the annotation array
 	 * @throws IllegalArgumentException if the attribute does not exist or
@@ -328,8 +322,8 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	 * component type of the expected array type, the single element will be
 	 * wrapped in a single-element array of the appropriate type before
 	 * returning it.
-	 * @param attributeName the name of the attribute to get; never
-	 * {@code null} or empty
+	 * @param attributeName the name of the attribute to get;
+	 * never {@code null} or empty
 	 * @param expectedType the expected type; never {@code null}
 	 * @return the value
 	 * @throws IllegalArgumentException if the attribute does not exist or
@@ -428,7 +422,8 @@ public class AnnotationAttributes extends LinkedHashMap<String, Object> {
 	 * to the {@link #AnnotationAttributes(Map)} constructor.
 	 * @param map original source of annotation attribute <em>key-value</em> pairs
 	 */
-	public static AnnotationAttributes fromMap(Map<String, Object> map) {
+	@Nullable
+	public static AnnotationAttributes fromMap(@Nullable Map<String, Object> map) {
 		if (map == null) {
 			return null;
 		}

spring-core/src/main/java/org/springframework/core/annotation/AnnotationAwareOrderComparator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -81,7 +81,7 @@ public class AnnotationAwareOrderComparator extends OrderComparator {
 				return ann.value();
 			}
 		}
-		else if (obj != null) {
+		else {
 			order = OrderUtils.getOrder(obj.getClass());
 			if (order == null && obj instanceof DecoratingProxy) {
 				order = OrderUtils.getOrder(((DecoratingProxy) obj).getDecoratedClass());
@@ -98,15 +98,12 @@ public class AnnotationAwareOrderComparator extends OrderComparator {
 	 * multiple matches but only one object to be returned.
 	 */
 	public Integer getPriority(Object obj) {
-		Integer priority = null;
 		if (obj instanceof Class) {
-			priority = OrderUtils.getPriority((Class<?>) obj);
+			return OrderUtils.getPriority((Class<?>) obj);
 		}
-		else if (obj != null) {
-			priority = OrderUtils.getPriority(obj.getClass());
-			if (priority == null && obj instanceof DecoratingProxy) {
-				priority = OrderUtils.getOrder(((DecoratingProxy) obj).getDecoratedClass());
-			}
+		Integer priority = OrderUtils.getPriority(obj.getClass());
+		if (priority == null && obj instanceof DecoratingProxy) {
+			priority = OrderUtils.getOrder(((DecoratingProxy) obj).getDecoratedClass());
 		}
 		return priority;
 	}

spring-core/src/main/java/org/springframework/core/annotation/AnnotationUtils.java

@@ -191,7 +191,7 @@ public abstract class AnnotationUtils {
 					}
 				}
 			}
-			return synthesizeAnnotation(annotation, annotatedElement);
+			return (annotation != null ? synthesizeAnnotation(annotation, annotatedElement) : null);
 		}
 		catch (Throwable ex) {
 			handleIntrospectionFailure(annotatedElement, ex);
@@ -231,7 +231,7 @@ public abstract class AnnotationUtils {
 	 * @see AnnotatedElement#getAnnotations()
 	 */
 	@Nullable
-	public static Annotation[] getAnnotations(@Nullable AnnotatedElement annotatedElement) {
+	public static Annotation[] getAnnotations(AnnotatedElement annotatedElement) {
 		try {
 			return synthesizeAnnotationArray(annotatedElement.getAnnotations(), annotatedElement);
 		}
@@ -473,14 +473,11 @@ public abstract class AnnotationUtils {
 	@Nullable
 	public static <A extends Annotation> A findAnnotation(AnnotatedElement annotatedElement, Class<A> annotationType) {
 		Assert.notNull(annotatedElement, "AnnotatedElement must not be null");
-		if (annotationType == null) {
-			return null;
-		}
 
 		// Do NOT store result in the findAnnotationCache since doing so could break
 		// findAnnotation(Class, Class) and findAnnotation(Method, Class).
 		A ann = findAnnotation(annotatedElement, annotationType, new HashSet<>());
-		return synthesizeAnnotation(ann, annotatedElement);
+		return (ann != null ? synthesizeAnnotation(ann, annotatedElement) : null);
 	}
 
 	/**
@@ -536,9 +533,6 @@ public abstract class AnnotationUtils {
 	@Nullable
 	public static <A extends Annotation> A findAnnotation(Method method, Class<A> annotationType) {
 		Assert.notNull(method, "Method must not be null");
-		if (annotationType == null) {
-			return null;
-		}
 
 		AnnotationCacheKey cacheKey = new AnnotationCacheKey(method, annotationType);
 		A result = (A) findAnnotationCache.get(cacheKey);
@@ -579,6 +573,7 @@ public abstract class AnnotationUtils {
 		return result;
 	}
 
+	@Nullable
 	private static <A extends Annotation> A searchOnInterfaces(Method method, Class<A> annotationType, Class<?>... ifcs) {
 		A annotation = null;
 		for (Class<?> iface : ifcs) {
@@ -660,10 +655,6 @@ public abstract class AnnotationUtils {
 	@Nullable
 	private static <A extends Annotation> A findAnnotation(Class<?> clazz, Class<A> annotationType, boolean synthesize) {
 		Assert.notNull(clazz, "Class must not be null");
-		if (annotationType == null) {
-			return null;
-		}
-
 		AnnotationCacheKey cacheKey = new AnnotationCacheKey(clazz, annotationType);
 		A result = (A) findAnnotationCache.get(cacheKey);
 		if (result == null) {
@@ -857,7 +848,7 @@ public abstract class AnnotationUtils {
 	 * @since 4.2.1
 	 */
 	public static boolean isAnnotationMetaPresent(Class<? extends Annotation> annotationType,
-			Class<? extends Annotation> metaAnnotationType) {
+			@Nullable Class<? extends Annotation> metaAnnotationType) {
 
 		Assert.notNull(annotationType, "Annotation type must not be null");
 		if (metaAnnotationType == null) {
@@ -883,7 +874,7 @@ public abstract class AnnotationUtils {
 	 * @param annotation the annotation to check
 	 * @return {@code true} if the annotation is in the {@code java.lang.annotation} package
 	 */
-	public static boolean isInJavaLangAnnotationPackage(Annotation annotation) {
+	public static boolean isInJavaLangAnnotationPackage(@Nullable Annotation annotation) {
 		return (annotation != null && isInJavaLangAnnotationPackage(annotation.annotationType()));
 	}
 
@@ -894,7 +885,7 @@ public abstract class AnnotationUtils {
 	 * @return {@code true} if the annotation is in the {@code java.lang.annotation} package
 	 * @since 4.3.8
 	 */
-	static boolean isInJavaLangAnnotationPackage(Class<? extends Annotation> annotationType) {
+	static boolean isInJavaLangAnnotationPackage(@Nullable Class<? extends Annotation> annotationType) {
 		return (annotationType != null && isInJavaLangAnnotationPackage(annotationType.getName()));
 	}
 
@@ -905,7 +896,7 @@ public abstract class AnnotationUtils {
 	 * @return {@code true} if the annotation is in the {@code java.lang.annotation} package
 	 * @since 4.2
 	 */
-	public static boolean isInJavaLangAnnotationPackage(String annotationType) {
+	public static boolean isInJavaLangAnnotationPackage(@Nullable String annotationType) {
 		return (annotationType != null && annotationType.startsWith("java.lang.annotation"));
 	}
 
@@ -1010,7 +1001,7 @@ public abstract class AnnotationUtils {
 				(Object) annotatedElement, annotation, classValuesAsString, nestedAnnotationsAsMap);
 	}
 
-	private static AnnotationAttributes getAnnotationAttributes(Object annotatedElement,
+	private static AnnotationAttributes getAnnotationAttributes(@Nullable Object annotatedElement,
 			Annotation annotation, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
 
 		AnnotationAttributes attributes =
@@ -1091,8 +1082,9 @@ public abstract class AnnotationUtils {
 	 * {@code Annotation} instances
 	 * @return the adapted value, or the original value if no adaptation is needed
 	 */
-	static Object adaptValue(@Nullable Object annotatedElement, Object value, boolean classValuesAsString,
-			boolean nestedAnnotationsAsMap) {
+	@Nullable
+	static Object adaptValue(@Nullable Object annotatedElement, @Nullable Object value,
+			boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
 
 		if (classValuesAsString) {
 			if (value instanceof Class) {
@@ -1215,9 +1207,8 @@ public abstract class AnnotationUtils {
 	 * @see #getDefaultValue(Class, String)
 	 */
 	static void postProcessAnnotationAttributes(@Nullable Object annotatedElement,
-			AnnotationAttributes attributes, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
+			@Nullable AnnotationAttributes attributes, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
 
-		// Abort?
 		if (attributes == null) {
 			return;
 		}
@@ -1256,7 +1247,7 @@ public abstract class AnnotationUtils {
 								throw new AnnotationConfigurationException(String.format(
 										"In AnnotationAttributes for annotation [%s] declared on %s, " +
 										"attribute '%s' and its alias '%s' are declared with values of [%s] and [%s], " +
-										"but only one is permitted.", annotationType.getName(), elementAsString,
+										"but only one is permitted.", attributes.displayName, elementAsString,
 										attributeName, aliasedAttributeName, ObjectUtils.nullSafeToString(value),
 										ObjectUtils.nullSafeToString(aliasedValue)));
 							}
@@ -1319,7 +1310,7 @@ public abstract class AnnotationUtils {
 	 */
 	@Nullable
 	public static Object getValue(Annotation annotation, String attributeName) {
-		if (annotation == null || !StringUtils.hasText(attributeName)) {
+		if (!StringUtils.hasText(attributeName)) {
 			return null;
 		}
 		try {
@@ -1359,9 +1350,6 @@ public abstract class AnnotationUtils {
 	 */
 	@Nullable
 	public static Object getDefaultValue(Annotation annotation, String attributeName) {
-		if (annotation == null) {
-			return null;
-		}
 		return getDefaultValue(annotation.annotationType(), attributeName);
 	}
 
@@ -1387,7 +1375,7 @@ public abstract class AnnotationUtils {
 	 */
 	@Nullable
 	public static Object getDefaultValue(Class<? extends Annotation> annotationType, String attributeName) {
-		if (annotationType == null || !StringUtils.hasText(attributeName)) {
+		if (!StringUtils.hasText(attributeName)) {
 			return null;
 		}
 		try {
@@ -1413,8 +1401,7 @@ public abstract class AnnotationUtils {
 	 * @since 4.2
 	 * @see #synthesizeAnnotation(Annotation, AnnotatedElement)
 	 */
-	@Nullable
-	static <A extends Annotation> A synthesizeAnnotation(@Nullable A annotation) {
+	static <A extends Annotation> A synthesizeAnnotation(A annotation) {
 		return synthesizeAnnotation(annotation, null);
 	}
 
@@ -1435,16 +1422,14 @@ public abstract class AnnotationUtils {
 	 * @see #synthesizeAnnotation(Map, Class, AnnotatedElement)
 	 * @see #synthesizeAnnotation(Class)
 	 */
-	@Nullable
-	public static <A extends Annotation> A synthesizeAnnotation(A annotation, @Nullable AnnotatedElement annotatedElement) {
+	public static <A extends Annotation> A synthesizeAnnotation(
+			A annotation, @Nullable AnnotatedElement annotatedElement) {
+
 		return synthesizeAnnotation(annotation, (Object) annotatedElement);
 	}
 
 	@SuppressWarnings("unchecked")
 	static <A extends Annotation> A synthesizeAnnotation(A annotation, @Nullable Object annotatedElement) {
-		if (annotation == null) {
-			return null;
-		}
 		if (annotation instanceof SynthesizedAnnotation) {
 			return annotation;
 		}
@@ -1496,7 +1481,7 @@ public abstract class AnnotationUtils {
 	 */
 	@SuppressWarnings("unchecked")
 	@Nullable
-	public static <A extends Annotation> A synthesizeAnnotation(Map<String, Object> attributes,
+	public static <A extends Annotation> A synthesizeAnnotation(@Nullable Map<String, Object> attributes,
 			Class<A> annotationType, @Nullable AnnotatedElement annotatedElement) {
 
 		Assert.notNull(annotationType, "'annotationType' must not be null");
@@ -1548,10 +1533,8 @@ public abstract class AnnotationUtils {
 	 * @see #synthesizeAnnotation(Annotation, AnnotatedElement)
 	 * @see #synthesizeAnnotation(Map, Class, AnnotatedElement)
 	 */
-	static Annotation[] synthesizeAnnotationArray(Annotation[] annotations, @Nullable Object annotatedElement) {
-		if (annotations == null) {
-			return null;
-		}
+	static Annotation[] synthesizeAnnotationArray(
+			Annotation[] annotations, @Nullable Object annotatedElement) {
 
 		Annotation[] synthesized = (Annotation[]) Array.newInstance(
 				annotations.getClass().getComponentType(), annotations.length);
@@ -1612,7 +1595,7 @@ public abstract class AnnotationUtils {
 	 * @return a map containing attribute aliases (never {@code null})
 	 * @since 4.2
 	 */
-	static Map<String, List<String>> getAttributeAliasMap(Class<? extends Annotation> annotationType) {
+	static Map<String, List<String>> getAttributeAliasMap(@Nullable Class<? extends Annotation> annotationType) {
 		if (annotationType == null) {
 			return Collections.emptyMap();
 		}
@@ -1796,7 +1779,7 @@ public abstract class AnnotationUtils {
 	 * @return {@code true} if the method is an attribute method
 	 * @since 4.2
 	 */
-	static boolean isAttributeMethod(Method method) {
+	static boolean isAttributeMethod(@Nullable Method method) {
 		return (method != null && method.getParameterCount() == 0 && method.getReturnType() != void.class);
 	}
 
@@ -1806,7 +1789,7 @@ public abstract class AnnotationUtils {
 	 * @see Annotation#annotationType()
 	 * @since 4.2
 	 */
-	static boolean isAnnotationTypeMethod(Method method) {
+	static boolean isAnnotationTypeMethod(@Nullable Method method) {
 		return (method != null && method.getName().equals("annotationType") && method.getParameterCount() == 0);
 	}
 
@@ -1852,7 +1835,7 @@ public abstract class AnnotationUtils {
 	 * @param ex the exception that we encountered
 	 * @see #rethrowAnnotationConfigurationException
 	 */
-	static void handleIntrospectionFailure(AnnotatedElement element, Throwable ex) {
+	static void handleIntrospectionFailure(@Nullable AnnotatedElement element, Throwable ex) {
 		rethrowAnnotationConfigurationException(ex);
 
 		Log loggerToUse = logger;
@@ -1934,7 +1917,9 @@ public abstract class AnnotationUtils {
 
 		private final Set<A> result = new LinkedHashSet<>();
 
-		AnnotationCollector(Class<A> annotationType, Class<? extends Annotation> containerAnnotationType, boolean declaredMode) {
+		AnnotationCollector(Class<A> annotationType,
+				@Nullable Class<? extends Annotation> containerAnnotationType, boolean declaredMode) {
+
 			this.annotationType = annotationType;
 			this.containerAnnotationType = (containerAnnotationType != null ? containerAnnotationType :
 					resolveContainerAnnotationType(annotationType));
@@ -1974,8 +1959,11 @@ public abstract class AnnotationUtils {
 		private List<A> getValue(AnnotatedElement element, Annotation annotation) {
 			try {
 				List<A> synthesizedAnnotations = new ArrayList<>();
-				for (A anno : (A[]) AnnotationUtils.getValue(annotation)) {
-					synthesizedAnnotations.add(synthesizeAnnotation(anno, element));
+				A[] value = (A[]) AnnotationUtils.getValue(annotation);
+				if (value != null) {
+					for (A anno : value) {
+						synthesizedAnnotations.add(synthesizeAnnotation(anno, element));
+					}
 				}
 				return synthesizedAnnotations;
 			}
@@ -2251,7 +2239,6 @@ public abstract class AnnotationUtils {
 		 * @throws AnnotationConfigurationException if invalid configuration of
 		 * {@code @AliasFor} is detected
 		 */
-		@Nullable
 		private String getAliasedAttributeName(AliasFor aliasFor, Method attribute) {
 			String attributeName = aliasFor.attribute();
 			String value = aliasFor.value();

spring-core/src/main/java/org/springframework/core/annotation/DefaultAnnotationAttributeExtractor.java

@@ -56,7 +56,7 @@ class DefaultAnnotationAttributeExtractor extends AbstractAliasAwareAnnotationAt
 	@Override
 	protected Object getRawAttributeValue(String attributeName) {
 		Method attributeMethod = ReflectionUtils.findMethod(getAnnotationType(), attributeName);
-		return getRawAttributeValue(attributeMethod);
+		return (attributeMethod != null ? getRawAttributeValue(attributeMethod) : null);
 	}
 
 }

spring-core/src/main/java/org/springframework/core/annotation/OrderUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,15 +48,17 @@ public abstract class OrderUtils {
 
 
 	/**
-	 * Return the order on the specified {@code type}.
+	 * Return the order on the specified {@code type}, or the specified
+	 * default value if none can be found.
 	 * <p>Takes care of {@link Order @Order} and {@code @javax.annotation.Priority}.
 	 * @param type the type to handle
-	 * @return the order value, or {@code null} if none can be found
+	 * @return the priority value, or the specified default order if none can be found
+	 * @since 5.0
 	 * @see #getPriority(Class)
 	 */
-	@Nullable
-	public static Integer getOrder(Class<?> type) {
-		return getOrder(type, null);
+	public static int getOrder(Class<?> type, int defaultOrder) {
+		Integer order = getOrder(type);
+		return (order != null ? order : defaultOrder);
 	}
 
 	/**
@@ -67,7 +69,21 @@ public abstract class OrderUtils {
 	 * @return the priority value, or the specified default order if none can be found
 	 * @see #getPriority(Class)
 	 */
-	public static Integer getOrder(Class<?> type, Integer defaultOrder) {
+	@Nullable
+	public static Integer getOrder(Class<?> type, @Nullable Integer defaultOrder) {
+		Integer order = getOrder(type);
+		return (order != null ? order : defaultOrder);
+	}
+
+	/**
+	 * Return the order on the specified {@code type}.
+	 * <p>Takes care of {@link Order @Order} and {@code @javax.annotation.Priority}.
+	 * @param type the type to handle
+	 * @return the order value, or {@code null} if none can be found
+	 * @see #getPriority(Class)
+	 */
+	@Nullable
+	public static Integer getOrder(Class<?> type) {
 		Order order = AnnotationUtils.findAnnotation(type, Order.class);
 		if (order != null) {
 			return order.value();
@@ -76,7 +92,7 @@ public abstract class OrderUtils {
 		if (priorityOrder != null) {
 			return priorityOrder;
 		}
-		return defaultOrder;
+		return null;
 	}
 
 	/**

spring-core/src/main/java/org/springframework/core/codec/AbstractSingleValueEncoder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -61,6 +61,6 @@ public abstract class AbstractSingleValueEncoder<T> extends AbstractEncoder<T> {
 	 * @return the output stream
 	 */
 	protected abstract Flux<DataBuffer> encode(T t, DataBufferFactory dataBufferFactory,
-			ResolvableType type, MimeType mimeType, Map<String, Object> hints);
+			ResolvableType type, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints);
 
 }

spring-core/src/main/java/org/springframework/core/codec/ByteArrayDecoder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,7 +48,7 @@ public class ByteArrayDecoder extends AbstractDecoder<byte[]> {
 	}
 
 	@Override
-	public Flux<byte[]> decode(Publisher<DataBuffer> inputStream,@Nullable  ResolvableType elementType,
+	public Flux<byte[]> decode(Publisher<DataBuffer> inputStream, ResolvableType elementType,
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
 
 		return Flux.from(inputStream).map((dataBuffer) -> {

spring-core/src/main/java/org/springframework/core/codec/ByteBufferDecoder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -46,11 +46,11 @@ public class ByteBufferDecoder extends AbstractDecoder<ByteBuffer> {
 	@Override
 	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
 		Class<?> clazz = elementType.getRawClass();
-		return (super.canDecode(elementType, mimeType) && ByteBuffer.class.isAssignableFrom(clazz));
+		return (super.canDecode(elementType, mimeType) && clazz != null && ByteBuffer.class.isAssignableFrom(clazz));
 	}
 
 	@Override
-	public Flux<ByteBuffer> decode(Publisher<DataBuffer> inputStream, @Nullable ResolvableType elementType,
+	public Flux<ByteBuffer> decode(Publisher<DataBuffer> inputStream, ResolvableType elementType,
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
 
 		return Flux.from(inputStream).map((dataBuffer) -> {

spring-core/src/main/java/org/springframework/core/codec/DataBufferDecoder.java

@@ -46,12 +46,13 @@ public class DataBufferDecoder extends AbstractDecoder<DataBuffer> {
 	@Override
 	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
 		Class<?> clazz = elementType.getRawClass();
-		return (super.canDecode(elementType, mimeType) && DataBuffer.class.isAssignableFrom(clazz));
+		return (super.canDecode(elementType, mimeType) && clazz != null && DataBuffer.class.isAssignableFrom(clazz));
 	}
 
 	@Override
-	public Flux<DataBuffer> decode(Publisher<DataBuffer> inputStream, @Nullable ResolvableType elementType,
+	public Flux<DataBuffer> decode(Publisher<DataBuffer> inputStream, ResolvableType elementType,
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
+
 		return Flux.from(inputStream);
 	}
 

spring-core/src/main/java/org/springframework/core/codec/Decoder.java

@@ -43,7 +43,8 @@ public interface Decoder<T> {
 	 * Whether the decoder supports the given target element type and the MIME
 	 * type of the source stream.
 	 * @param elementType the target element type for the output stream
-	 * @param mimeType the mime type associated with the stream to decode, can be {@code null} if not specified.
+	 * @param mimeType the mime type associated with the stream to decode
+	 * (can be {@code null} if not specified)
 	 * @return {@code true} if supported, {@code false} otherwise
 	 */
 	boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType);
@@ -54,11 +55,11 @@ public interface Decoder<T> {
 	 * @param elementType the expected type of elements in the output stream;
 	 * this type must have been previously passed to the {@link #canDecode}
 	 * method and it must have returned {@code true}.
-	 * @param mimeType the MIME type associated with the input stream, optional
+	 * @param mimeType the MIME type associated with the input stream (optional)
 	 * @param hints additional information about how to do encode
 	 * @return the output stream with decoded elements
 	 */
-	Flux<T> decode(Publisher<DataBuffer> inputStream, @Nullable ResolvableType elementType,
+	Flux<T> decode(Publisher<DataBuffer> inputStream, ResolvableType elementType,
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints);
 
 	/**
@@ -67,7 +68,7 @@ public interface Decoder<T> {
 	 * @param elementType the expected type of elements in the output stream;
 	 * this type must have been previously passed to the {@link #canDecode}
 	 * method and it must have returned {@code true}.
-	 * @param mimeType the MIME type associated with the input stream, optional
+	 * @param mimeType the MIME type associated with the input stream (optional)
 	 * @param hints additional information about how to do encode
 	 * @return the output stream with the decoded element
 	 */

spring-core/src/main/java/org/springframework/core/codec/Encoder.java

@@ -44,7 +44,8 @@ public interface Encoder<T> {
 	 * Whether the encoder supports the given source element type and the MIME
 	 * type for the output stream.
 	 * @param elementType the type of elements in the source stream
-	 * @param mimeType the MIME type for the output stream, can be {@code null} if not specified.
+	 * @param mimeType the MIME type for the output stream
+	 * (can be {@code null} if not specified)
 	 * @return {@code true} if supported, {@code false} otherwise
 	 */
 	boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType);
@@ -59,7 +60,7 @@ public interface Encoder<T> {
 	 * @param elementType the expected type of elements in the input stream;
 	 * this type must have been previously passed to the {@link #canEncode}
 	 * method and it must have returned {@code true}.
-	 * @param mimeType the MIME type for the output stream
+	 * @param mimeType the MIME type for the output stream (optional)
 	 * @param hints additional information about how to do encode
 	 * @return the output stream
 	 */

spring-core/src/main/java/org/springframework/core/codec/ResourceDecoder.java

@@ -30,6 +30,7 @@ import org.springframework.core.io.Resource;
 import org.springframework.core.io.buffer.DataBuffer;
 import org.springframework.core.io.buffer.DataBufferUtils;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.MimeType;
 import org.springframework.util.MimeTypeUtils;
 
@@ -49,13 +50,13 @@ public class ResourceDecoder extends AbstractDecoder<Resource> {
 	@Override
 	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
 		Class<?> clazz = elementType.getRawClass();
-		return (InputStreamResource.class.equals(clazz) ||
-				clazz.isAssignableFrom(ByteArrayResource.class)) &&
-				super.canDecode(elementType, mimeType);
+		return (clazz != null &&
+				(InputStreamResource.class == clazz || clazz.isAssignableFrom(ByteArrayResource.class)) &&
+				super.canDecode(elementType, mimeType));
 	}
 
 	@Override
-	public Flux<Resource> decode(Publisher<DataBuffer> inputStream, @Nullable ResolvableType elementType,
+	public Flux<Resource> decode(Publisher<DataBuffer> inputStream, ResolvableType elementType,
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
 
 		return Flux.from(decodeToMono(inputStream, elementType, mimeType, hints));
@@ -66,6 +67,7 @@ public class ResourceDecoder extends AbstractDecoder<Resource> {
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
 
 		Class<?> clazz = elementType.getRawClass();
+		Assert.state(clazz != null, "No resource class");
 
 		Mono<byte[]> byteArray = Flux.from(inputStream).
 				reduce(DataBuffer::write).
@@ -77,7 +79,7 @@ public class ResourceDecoder extends AbstractDecoder<Resource> {
 				});
 
 
-		if (InputStreamResource.class.equals(clazz)) {
+		if (InputStreamResource.class == clazz) {
 			return Mono.from(byteArray.map(ByteArrayInputStream::new).map(InputStreamResource::new));
 		}
 		else if (clazz.isAssignableFrom(ByteArrayResource.class)) {

spring-core/src/main/java/org/springframework/core/codec/ResourceEncoder.java

@@ -68,7 +68,7 @@ public class ResourceEncoder extends AbstractSingleValueEncoder<Resource> {
 
 	@Override
 	protected Flux<DataBuffer> encode(Resource resource, DataBufferFactory dataBufferFactory,
-			ResolvableType type, MimeType mimeType, Map<String, Object> hints) {
+			ResolvableType type, MimeType mimeType, @Nullable Map<String, Object> hints) {
 
 		try {
 			if (resource.isFile()) {

spring-core/src/main/java/org/springframework/core/codec/ResourceRegionEncoder.java

@@ -77,7 +77,8 @@ public class ResourceRegionEncoder extends AbstractEncoder<ResourceRegion> {
 	@Override
 	@SuppressWarnings("unchecked")
 	public Flux<DataBuffer> encode(Publisher<? extends ResourceRegion> inputStream,
-			DataBufferFactory bufferFactory, ResolvableType elementType, @Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
+			DataBufferFactory bufferFactory, ResolvableType elementType, @Nullable MimeType mimeType,
+			@Nullable Map<String, Object> hints) {
 
 		Assert.notNull(inputStream, "'inputStream' must not be null");
 		Assert.notNull(bufferFactory, "'bufferFactory' must not be null");
@@ -93,7 +94,8 @@ public class ResourceRegionEncoder extends AbstractEncoder<ResourceRegion> {
 			final String boundaryString = (String) hints.get(BOUNDARY_STRING_HINT);
 
 			byte[] startBoundary = getAsciiBytes("\r\n--" + boundaryString + "\r\n");
-			byte[] contentType = getAsciiBytes("Content-Type: " + mimeType.toString() + "\r\n");
+			byte[] contentType =
+					(mimeType != null ? getAsciiBytes("Content-Type: " + mimeType + "\r\n") : new byte[0]);
 
 			Flux<DataBuffer> regions = Flux.from(inputStream).
 					concatMap(region ->

spring-core/src/main/java/org/springframework/core/codec/StringDecoder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -77,7 +77,7 @@ public class StringDecoder extends AbstractDecoder<String> {
 	}
 
 	@Override
-	public Flux<String> decode(Publisher<DataBuffer> inputStream, @Nullable ResolvableType elementType,
+	public Flux<String> decode(Publisher<DataBuffer> inputStream, ResolvableType elementType,
 			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {
 
 		Flux<DataBuffer> inputFlux = Flux.from(inputStream);
@@ -113,14 +113,14 @@ public class StringDecoder extends AbstractDecoder<String> {
 		return Flux.fromIterable(results);
 	}
 
-	private String decodeDataBuffer(DataBuffer dataBuffer, MimeType mimeType) {
+	private String decodeDataBuffer(DataBuffer dataBuffer, @Nullable MimeType mimeType) {
 		Charset charset = getCharset(mimeType);
 		CharBuffer charBuffer = charset.decode(dataBuffer.asByteBuffer());
 		DataBufferUtils.release(dataBuffer);
 		return charBuffer.toString();
 	}
 
-	private Charset getCharset(MimeType mimeType) {
+	private Charset getCharset(@Nullable MimeType mimeType) {
 		if (mimeType != null && mimeType.getCharset() != null) {
 			return mimeType.getCharset();
 		}

spring-core/src/main/java/org/springframework/core/convert/ConversionFailedException.java

@@ -43,7 +43,9 @@ public class ConversionFailedException extends ConversionException {
 	 * @param value the value we tried to convert
 	 * @param cause the cause of the conversion failure
 	 */
-	public ConversionFailedException(TypeDescriptor sourceType, TypeDescriptor targetType, @Nullable Object value, Throwable cause) {
+	public ConversionFailedException(@Nullable TypeDescriptor sourceType, TypeDescriptor targetType,
+			@Nullable Object value, Throwable cause) {
+
 		super("Failed to convert from type [" + sourceType + "] to type [" + targetType +
 				"] for value '" + ObjectUtils.nullSafeToString(value) + "'", cause);
 		this.sourceType = sourceType;

spring-core/src/main/java/org/springframework/core/convert/ConversionService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -72,6 +72,7 @@ public interface ConversionService {
 	 * @throws ConversionException if a conversion exception occurred
 	 * @throws IllegalArgumentException if targetType is {@code null}
 	 */
+	@Nullable
 	<T> T convert(@Nullable Object source, Class<T> targetType);
 
 	/**
@@ -87,6 +88,7 @@ public interface ConversionService {
 	 * @throws IllegalArgumentException if targetType is {@code null},
 	 * or {@code sourceType} is {@code null} but source is not {@code null}
 	 */
+	@Nullable
 	Object convert(@Nullable Object source, @Nullable TypeDescriptor sourceType, TypeDescriptor targetType);
 
 }

spring-core/src/main/java/org/springframework/core/convert/ConverterNotFoundException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,8 @@
 
 package org.springframework.core.convert;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Exception to be thrown when a suitable converter could not be found
  * in a given conversion service.
@@ -37,7 +39,7 @@ public class ConverterNotFoundException extends ConversionException {
 	 * @param sourceType the source type requested to convert from
 	 * @param targetType the target type requested to convert to
 	 */
-	public ConverterNotFoundException(TypeDescriptor sourceType, TypeDescriptor targetType) {
+	public ConverterNotFoundException(@Nullable TypeDescriptor sourceType, TypeDescriptor targetType) {
 		super("No converter found capable of converting from type [" + sourceType + "] to type [" + targetType + "]");
 		this.sourceType = sourceType;
 		this.targetType = targetType;
@@ -47,6 +49,7 @@ public class ConverterNotFoundException extends ConversionException {
 	/**
 	 * Return the source type that was requested to convert from.
 	 */
+	@Nullable
 	public TypeDescriptor getSourceType() {
 		return this.sourceType;
 	}

spring-core/src/main/java/org/springframework/core/convert/Property.java

@@ -67,7 +67,9 @@ public final class Property {
 		this(objectType, readMethod, writeMethod, null);
 	}
 
-	public Property(Class<?> objectType, Method readMethod, Method writeMethod, String name) {
+	public Property(
+			Class<?> objectType, @Nullable Method readMethod, @Nullable Method writeMethod, @Nullable String name) {
+
 		this.objectType = objectType;
 		this.readMethod = readMethod;
 		this.writeMethod = writeMethod;
@@ -100,6 +102,7 @@ public final class Property {
 	/**
 	 * The property getter method: e.g. {@code getFoo()}
 	 */
+	@Nullable
 	public Method getReadMethod() {
 		return this.readMethod;
 	}
@@ -107,6 +110,7 @@ public final class Property {
 	/**
 	 * The property setter method: e.g. {@code setFoo(String)}
 	 */
+	@Nullable
 	public Method getWriteMethod() {
 		return this.writeMethod;
 	}
@@ -208,8 +212,8 @@ public final class Property {
 	}
 
 	private void addAnnotationsToMap(
-		Map<Class<? extends Annotation>, Annotation> annotationMap,
-		AnnotatedElement object) {
+			Map<Class<? extends Annotation>, Annotation> annotationMap, @Nullable AnnotatedElement object) {
+
 		if (object != null) {
 			for (Annotation annotation : object.getAnnotations()) {
 				annotationMap.put(annotation.annotationType(), annotation);
@@ -223,27 +227,34 @@ public final class Property {
 		if (!StringUtils.hasLength(name)) {
 			return null;
 		}
+		Field field = null;
 		Class<?> declaringClass = declaringClass();
-		Field field = ReflectionUtils.findField(declaringClass, name);
-		if (field == null) {
-			// Same lenient fallback checking as in CachedIntrospectionResults...
-			field = ReflectionUtils.findField(declaringClass,
-					name.substring(0, 1).toLowerCase() + name.substring(1));
+		if (declaringClass != null) {
+			field = ReflectionUtils.findField(declaringClass, name);
 			if (field == null) {
+				// Same lenient fallback checking as in CachedIntrospectionResults...
 				field = ReflectionUtils.findField(declaringClass,
-						name.substring(0, 1).toUpperCase() + name.substring(1));
+						name.substring(0, 1).toLowerCase() + name.substring(1));
+				if (field == null) {
+					field = ReflectionUtils.findField(declaringClass,
+							name.substring(0, 1).toUpperCase() + name.substring(1));
+				}
 			}
 		}
 		return field;
 	}
 
+	@Nullable
 	private Class<?> declaringClass() {
 		if (getReadMethod() != null) {
 			return getReadMethod().getDeclaringClass();
 		}
-		else {
+		else if (getWriteMethod() != null) {
 			return getWriteMethod().getDeclaringClass();
 		}
+		else {
+			return null;
+		}
 	}
 
 

spring-core/src/main/java/org/springframework/core/convert/TypeDescriptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -163,7 +163,7 @@ public class TypeDescriptor implements Serializable {
 	 * @since 4.0
 	 */
 	public Object getSource() {
-		return (this.resolvableType != null ? this.resolvableType.getSource() : null);
+		return this.resolvableType.getSource();
 	}
 
 	/**
@@ -282,7 +282,7 @@ public class TypeDescriptor implements Serializable {
 			return false;
 		}
 		if (isArray() && typeDescriptor.isArray()) {
-			return getElementTypeDescriptor().isAssignableTo(typeDescriptor.getElementTypeDescriptor());
+			return isNestedAssignable(getElementTypeDescriptor(), typeDescriptor.getElementTypeDescriptor());
 		}
 		else if (isCollection() && typeDescriptor.isCollection()) {
 			return isNestedAssignable(getElementTypeDescriptor(), typeDescriptor.getElementTypeDescriptor());
@@ -296,11 +296,11 @@ public class TypeDescriptor implements Serializable {
 		}
 	}
 
-	private boolean isNestedAssignable(TypeDescriptor nestedTypeDescriptor, TypeDescriptor otherNestedTypeDescriptor) {
-		if (nestedTypeDescriptor == null || otherNestedTypeDescriptor == null) {
-			return true;
-		}
-		return nestedTypeDescriptor.isAssignableTo(otherNestedTypeDescriptor);
+	private boolean isNestedAssignable(@Nullable TypeDescriptor nestedTypeDescriptor,
+			@Nullable TypeDescriptor otherNestedTypeDescriptor) {
+
+		return (nestedTypeDescriptor == null || otherNestedTypeDescriptor == null ||
+				nestedTypeDescriptor.isAssignableTo(otherNestedTypeDescriptor));
 	}
 
 	/**
@@ -355,6 +355,7 @@ public class TypeDescriptor implements Serializable {
 	 * or array type
 	 * @see #narrow(Object)
 	 */
+	@Nullable
 	public TypeDescriptor elementTypeDescriptor(Object element) {
 		return narrow(element, getElementTypeDescriptor());
 	}
@@ -397,6 +398,7 @@ public class TypeDescriptor implements Serializable {
 	 * @throws IllegalStateException if this type is not a {@code java.util.Map}
 	 * @see #narrow(Object)
 	 */
+	@Nullable
 	public TypeDescriptor getMapKeyTypeDescriptor(Object mapKey) {
 		return narrow(mapKey, getMapKeyTypeDescriptor());
 	}
@@ -433,12 +435,13 @@ public class TypeDescriptor implements Serializable {
 	 * @throws IllegalStateException if this type is not a {@code java.util.Map}
 	 * @see #narrow(Object)
 	 */
+	@Nullable
 	public TypeDescriptor getMapValueTypeDescriptor(Object mapValue) {
 		return narrow(mapValue, getMapValueTypeDescriptor());
 	}
 
 	@Nullable
-	private TypeDescriptor narrow(Object value, TypeDescriptor typeDescriptor) {
+	private TypeDescriptor narrow(@Nullable Object value, @Nullable TypeDescriptor typeDescriptor) {
 		if (typeDescriptor != null) {
 			return typeDescriptor.narrow(value);
 		}
@@ -559,7 +562,7 @@ public class TypeDescriptor implements Serializable {
 	 * used to convert collection elements
 	 * @return the collection type descriptor
 	 */
-	public static TypeDescriptor collection(Class<?> collectionType, TypeDescriptor elementTypeDescriptor) {
+	public static TypeDescriptor collection(Class<?> collectionType, @Nullable TypeDescriptor elementTypeDescriptor) {
 		Assert.notNull(collectionType, "Collection type must not be null");
 		if (!Collection.class.isAssignableFrom(collectionType)) {
 			throw new IllegalArgumentException("Collection type must be a [java.util.Collection]");
@@ -582,7 +585,9 @@ public class TypeDescriptor implements Serializable {
 	 * @param valueTypeDescriptor the map's value type, used to convert map values
 	 * @return the map type descriptor
 	 */
-	public static TypeDescriptor map(Class<?> mapType, TypeDescriptor keyTypeDescriptor, TypeDescriptor valueTypeDescriptor) {
+	public static TypeDescriptor map(Class<?> mapType, @Nullable TypeDescriptor keyTypeDescriptor,
+			@Nullable TypeDescriptor valueTypeDescriptor) {
+
 		Assert.notNull(mapType, "Map type must not be null");
 		if (!Map.class.isAssignableFrom(mapType)) {
 			throw new IllegalArgumentException("Map type must be a [java.util.Map]");
@@ -730,7 +735,7 @@ public class TypeDescriptor implements Serializable {
 
 		private final Annotation[] annotations;
 
-		public AnnotatedElementAdapter(Annotation[] annotations) {
+		public AnnotatedElementAdapter(@Nullable Annotation[] annotations) {
 			this.annotations = annotations;
 		}
 
@@ -745,6 +750,7 @@ public class TypeDescriptor implements Serializable {
 		}
 
 		@Override
+		@Nullable
 		@SuppressWarnings("unchecked")
 		public <T extends Annotation> T getAnnotation(Class<T> annotationClass) {
 			for (Annotation annotation : getAnnotations()) {

spring-core/src/main/java/org/springframework/core/convert/converter/GenericConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -97,7 +97,7 @@ public interface GenericConverter {
 		}
 
 		@Override
-		public boolean equals(Object other) {
+		public boolean equals(@Nullable Object other) {
 			if (this == other) {
 				return true;
 			}

spring-core/src/main/java/org/springframework/core/convert/support/ArrayToArrayConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -61,10 +61,13 @@ final class ArrayToArrayConverter implements ConditionalGenericConverter {
 
 	@Override
 	public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
-		if (this.conversionService instanceof GenericConversionService &&
-				((GenericConversionService) this.conversionService).canBypassConvert(
-						sourceType.getElementTypeDescriptor(), targetType.getElementTypeDescriptor())) {
-			return source;
+		if (this.conversionService instanceof GenericConversionService) {
+			TypeDescriptor targetElement = targetType.getElementTypeDescriptor();
+			if (targetElement != null &&
+					((GenericConversionService) this.conversionService).canBypassConvert(
+							sourceType.getElementTypeDescriptor(), targetElement)) {
+				return source;
+			}
 		}
 		List<Object> sourceList = Arrays.asList(ObjectUtils.toObjectArray(source));
 		return this.helperConverter.convert(sourceList, sourceType, targetType);

spring-core/src/main/java/org/springframework/core/convert/support/ByteBufferConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -100,6 +100,7 @@ final class ByteBufferConverter implements ConditionalGenericConverter {
 		throw new IllegalStateException("Unexpected source/target types");
 	}
 
+	@Nullable
 	private Object convertFromByteBuffer(ByteBuffer source, TypeDescriptor targetType) {
 		byte[] bytes = new byte[source.remaining()];
 		source.get(bytes);
@@ -110,10 +111,14 @@ final class ByteBufferConverter implements ConditionalGenericConverter {
 		return this.conversionService.convert(bytes, BYTE_ARRAY_TYPE, targetType);
 	}
 
-	private Object convertToByteBuffer(Object source, TypeDescriptor sourceType) {
+	private Object convertToByteBuffer(@Nullable Object source, TypeDescriptor sourceType) {
 		byte[] bytes = (byte[]) (source instanceof byte[] ? source :
 				this.conversionService.convert(source, sourceType, BYTE_ARRAY_TYPE));
 
+		if (bytes == null) {
+			return ByteBuffer.wrap(new byte[0]);
+		}
+
 		ByteBuffer byteBuffer = ByteBuffer.allocate(bytes.length);
 		byteBuffer.put(bytes);
 

spring-core/src/main/java/org/springframework/core/convert/support/CollectionToArrayConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.convert.converter.ConditionalGenericConverter;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 
 /**
  * Converts a Collection to an array.
@@ -35,16 +36,19 @@ import org.springframework.lang.Nullable;
  * array's component type if necessary.
  *
  * @author Keith Donald
+ * @author Juergen Hoeller
  * @since 3.0
  */
 final class CollectionToArrayConverter implements ConditionalGenericConverter {
 
 	private final ConversionService conversionService;
 
+
 	public CollectionToArrayConverter(ConversionService conversionService) {
 		this.conversionService = conversionService;
 	}
 
+
 	@Override
 	public Set<ConvertiblePair> getConvertibleTypes() {
 		return Collections.singleton(new ConvertiblePair(Collection.class, Object[].class));
@@ -52,7 +56,8 @@ final class CollectionToArrayConverter implements ConditionalGenericConverter {
 
 	@Override
 	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
-		return ConversionUtils.canConvertElements(sourceType.getElementTypeDescriptor(), targetType.getElementTypeDescriptor(), this.conversionService);
+		return ConversionUtils.canConvertElements(sourceType.getElementTypeDescriptor(),
+				targetType.getElementTypeDescriptor(), this.conversionService);
 	}
 
 	@Override
@@ -62,10 +67,13 @@ final class CollectionToArrayConverter implements ConditionalGenericConverter {
 			return null;
 		}
 		Collection<?> sourceCollection = (Collection<?>) source;
-		Object array = Array.newInstance(targetType.getElementTypeDescriptor().getType(), sourceCollection.size());
+		TypeDescriptor targetElementType = targetType.getElementTypeDescriptor();
+		Assert.state(targetElementType != null, "No target element type");
+		Object array = Array.newInstance(targetElementType.getType(), sourceCollection.size());
 		int i = 0;
 		for (Object sourceElement : sourceCollection) {
-			Object targetElement = this.conversionService.convert(sourceElement, sourceType.elementTypeDescriptor(sourceElement), targetType.getElementTypeDescriptor());
+			Object targetElement = this.conversionService.convert(sourceElement,
+					sourceType.elementTypeDescriptor(sourceElement), targetElementType);
 			Array.set(array, i++, targetElement);
 		}
 		return array;

spring-core/src/main/java/org/springframework/core/convert/support/ConversionServiceFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@ import org.springframework.core.convert.converter.Converter;
 import org.springframework.core.convert.converter.ConverterFactory;
 import org.springframework.core.convert.converter.ConverterRegistry;
 import org.springframework.core.convert.converter.GenericConverter;
+import org.springframework.lang.Nullable;
 
 /**
  * A factory for common {@link org.springframework.core.convert.ConversionService}
@@ -40,7 +41,7 @@ public abstract class ConversionServiceFactory {
 	 * {@link ConverterFactory}, or {@link GenericConverter}
 	 * @param registry the target registry
 	 */
-	public static void registerConverters(Set<?> converters, ConverterRegistry registry) {
+	public static void registerConverters(@Nullable Set<?> converters, ConverterRegistry registry) {
 		if (converters != null) {
 			for (Object converter : converters) {
 				if (converter instanceof GenericConverter) {

spring-core/src/main/java/org/springframework/core/convert/support/ConversionUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import org.springframework.core.convert.ConversionFailedException;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.convert.converter.GenericConverter;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -31,8 +32,9 @@ import org.springframework.util.Assert;
  */
 abstract class ConversionUtils {
 
-	public static Object invokeConverter(GenericConverter converter, Object source, TypeDescriptor sourceType,
-			TypeDescriptor targetType) {
+	@Nullable
+	public static Object invokeConverter(GenericConverter converter, @Nullable Object source,
+			TypeDescriptor sourceType, TypeDescriptor targetType) {
 
 		try {
 			return converter.convert(source, sourceType, targetType);
@@ -45,8 +47,8 @@ abstract class ConversionUtils {
 		}
 	}
 
-	public static boolean canConvertElements(TypeDescriptor sourceElementType, TypeDescriptor targetElementType,
-			ConversionService conversionService) {
+	public static boolean canConvertElements(@Nullable TypeDescriptor sourceElementType,
+			@Nullable TypeDescriptor targetElementType, ConversionService conversionService) {
 
 		if (targetElementType == null) {
 			// yes

spring-core/src/main/java/org/springframework/core/convert/support/ConvertingPropertyEditorAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.beans.PropertyEditorSupport;
 
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -60,6 +61,7 @@ public class ConvertingPropertyEditorAdapter extends PropertyEditorSupport {
 	}
 
 	@Override
+	@Nullable
 	public String getAsText() {
 		if (this.canConvertToString) {
 			return (String) this.conversionService.convert(getValue(), this.targetDescriptor, TypeDescriptor.valueOf(String.class));

spring-core/src/main/java/org/springframework/core/convert/support/GenericConversionService.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -46,7 +46,6 @@ import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ConcurrentReferenceHashMap;
-import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -118,7 +117,7 @@ public class GenericConversionService implements ConfigurableConversionService {
 					"ConverterFactory [" + factory.getClass().getName() + "]; does the class parameterize those types?");
 		}
 		addConverter(new ConverterFactoryAdapter(factory,
-				new ConvertiblePair(typeInfo[0].resolve(), typeInfo[1].resolve())));
+				new ConvertiblePair(typeInfo[0].resolve(Object.class), typeInfo[1].resolve(Object.class))));
 	}
 
 	@Override
@@ -306,25 +305,29 @@ public class GenericConversionService implements ConfigurableConversionService {
 	}
 
 	@Nullable
-	private Object handleConverterNotFound(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
+	private Object handleConverterNotFound(
+			@Nullable Object source, @Nullable TypeDescriptor sourceType, TypeDescriptor targetType) {
+
 		if (source == null) {
 			assertNotPrimitiveTargetType(sourceType, targetType);
 			return null;
 		}
-		if (sourceType.isAssignableTo(targetType) && targetType.getObjectType().isInstance(source)) {
+		if ((sourceType == null || sourceType.isAssignableTo(targetType)) &&
+				targetType.getObjectType().isInstance(source)) {
 			return source;
 		}
 		throw new ConverterNotFoundException(sourceType, targetType);
 	}
 
-	private Object handleResult(@Nullable TypeDescriptor sourceType, TypeDescriptor targetType, Object result) {
+	@Nullable
+	private Object handleResult(@Nullable TypeDescriptor sourceType, TypeDescriptor targetType, @Nullable Object result) {
 		if (result == null) {
 			assertNotPrimitiveTargetType(sourceType, targetType);
 		}
 		return result;
 	}
 
-	private void assertNotPrimitiveTargetType(TypeDescriptor sourceType, TypeDescriptor targetType) {
+	private void assertNotPrimitiveTargetType(@Nullable TypeDescriptor sourceType, TypeDescriptor targetType) {
 		if (targetType.isPrimitive()) {
 			throw new ConversionFailedException(sourceType, targetType, null,
 					new IllegalArgumentException("A null value cannot be assigned to a primitive type"));
@@ -460,14 +463,13 @@ public class GenericConversionService implements ConfigurableConversionService {
 				return false;
 			}
 			ConverterCacheKey otherKey = (ConverterCacheKey) other;
-			return (ObjectUtils.nullSafeEquals(this.sourceType, otherKey.sourceType) &&
-					ObjectUtils.nullSafeEquals(this.targetType, otherKey.targetType));
+			return (this.sourceType.equals(otherKey.sourceType)) &&
+					this.targetType.equals(otherKey.targetType);
 		}
 
 		@Override
 		public int hashCode() {
-			return (ObjectUtils.nullSafeHashCode(this.sourceType) * 29 +
-					ObjectUtils.nullSafeHashCode(this.targetType));
+			return (this.sourceType.hashCode() * 29 + this.targetType.hashCode());
 		}
 
 		@Override

spring-core/src/main/java/org/springframework/core/convert/support/IdToEntityConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.convert.converter.ConditionalGenericConverter;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ReflectionUtils;
 
@@ -68,6 +69,7 @@ final class IdToEntityConverter implements ConditionalGenericConverter {
 			return null;
 		}
 		Method finder = getFinder(targetType.getType());
+		Assert.state(finder != null, "No finder method");
 		Object id = this.conversionService.convert(
 				source, sourceType, TypeDescriptor.valueOf(finder.getParameterTypes()[0]));
 		return ReflectionUtils.invokeMethod(finder, source, id);

spring-core/src/main/java/org/springframework/core/convert/support/MapToMapConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -113,14 +113,16 @@ final class MapToMapConverter implements ConditionalGenericConverter {
 				targetType.getMapValueTypeDescriptor(), this.conversionService);
 	}
 
-	private Object convertKey(Object sourceKey, TypeDescriptor sourceType, TypeDescriptor targetType) {
+	@Nullable
+	private Object convertKey(Object sourceKey, TypeDescriptor sourceType, @Nullable TypeDescriptor targetType) {
 		if (targetType == null) {
 			return sourceKey;
 		}
 		return this.conversionService.convert(sourceKey, sourceType.getMapKeyTypeDescriptor(sourceKey), targetType);
 	}
 
-	private Object convertValue(Object sourceValue, TypeDescriptor sourceType, TypeDescriptor targetType) {
+	@Nullable
+	private Object convertValue(Object sourceValue, TypeDescriptor sourceType, @Nullable TypeDescriptor targetType) {
 		if (targetType == null) {
 			return sourceValue;
 		}
@@ -134,7 +136,7 @@ final class MapToMapConverter implements ConditionalGenericConverter {
 
 		private final Object value;
 
-		public MapEntry(Object key, Object value) {
+		public MapEntry(@Nullable Object key, @Nullable Object value) {
 			this.key = key;
 			this.value = value;
 		}

spring-core/src/main/java/org/springframework/core/convert/support/ObjectToArrayConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,12 +24,14 @@ import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.convert.converter.ConditionalGenericConverter;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 
 /**
  * Converts an Object to a single-element array containing the Object.
  * Will convert the Object to the target array's component type if necessary.
  *
  * @author Keith Donald
+ * @author Juergen Hoeller
  * @since 3.0
  */
 final class ObjectToArrayConverter implements ConditionalGenericConverter {
@@ -49,7 +51,8 @@ final class ObjectToArrayConverter implements ConditionalGenericConverter {
 
 	@Override
 	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
-		return ConversionUtils.canConvertElements(sourceType, targetType.getElementTypeDescriptor(), this.conversionService);
+		return ConversionUtils.canConvertElements(sourceType, targetType.getElementTypeDescriptor(),
+				this.conversionService);
 	}
 
 	@Override
@@ -58,8 +61,10 @@ final class ObjectToArrayConverter implements ConditionalGenericConverter {
 		if (source == null) {
 			return null;
 		}
-		Object target = Array.newInstance(targetType.getElementTypeDescriptor().getType(), 1);
-		Object targetElement = this.conversionService.convert(source, sourceType, targetType.getElementTypeDescriptor());
+		TypeDescriptor targetElementType = targetType.getElementTypeDescriptor();
+		Assert.state(targetElementType != null, "No target element type");
+		Object target = Array.newInstance(targetElementType.getType(), 1);
+		Object targetElement = this.conversionService.convert(source, sourceType, targetElementType);
 		Array.set(target, 0, targetElement);
 		return target;
 	}

spring-core/src/main/java/org/springframework/core/convert/support/ObjectToObjectConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -193,6 +193,7 @@ final class ObjectToObjectConverter implements ConditionalGenericConverter {
 		return method;
 	}
 
+	@Nullable
 	private static Constructor<?> determineFactoryConstructor(Class<?> targetClass, Class<?> sourceClass) {
 		return ClassUtils.getConstructorIfAvailable(targetClass, sourceClass);
 	}

spring-core/src/main/java/org/springframework/core/convert/support/ObjectToOptionalConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -51,7 +51,7 @@ final class ObjectToOptionalConverter implements ConditionalGenericConverter {
 
 	@Override
 	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
-		if (targetType.getResolvableType() != null) {
+		if (targetType.getResolvableType().hasGenerics()) {
 			return this.conversionService.canConvert(sourceType, new GenericTypeDescriptor(targetType));
 		}
 		else {
@@ -68,7 +68,7 @@ final class ObjectToOptionalConverter implements ConditionalGenericConverter {
 		else if (source instanceof Optional) {
 			return source;
 		}
-		else if (targetType.getResolvableType() != null) {
+		else if (targetType.getResolvableType().hasGenerics()) {
 			Object target = this.conversionService.convert(source, sourceType, new GenericTypeDescriptor(targetType));
 			return Optional.ofNullable(target);
 		}
@@ -82,7 +82,7 @@ final class ObjectToOptionalConverter implements ConditionalGenericConverter {
 	private static class GenericTypeDescriptor extends TypeDescriptor {
 
 		public GenericTypeDescriptor(TypeDescriptor typeDescriptor) {
-			super(typeDescriptor.getResolvableType().getGeneric(0), null, typeDescriptor.getAnnotations());
+			super(typeDescriptor.getResolvableType().getGeneric(), null, typeDescriptor.getAnnotations());
 		}
 	}
 

spring-core/src/main/java/org/springframework/core/convert/support/StreamConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 package org.springframework.core.convert.support;
 
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
@@ -71,7 +72,7 @@ class StreamConverter implements ConditionalGenericConverter {
 	 * @param elementType the type of the stream elements
 	 * @param targetType the type to convert to
 	 */
-	public boolean matchesFromStream(TypeDescriptor elementType, TypeDescriptor targetType) {
+	public boolean matchesFromStream(@Nullable TypeDescriptor elementType, TypeDescriptor targetType) {
 		TypeDescriptor collectionOfElement = TypeDescriptor.collection(Collection.class, elementType);
 		return this.conversionService.canConvert(collectionOfElement, targetType);
 	}
@@ -82,7 +83,7 @@ class StreamConverter implements ConditionalGenericConverter {
 	 * @param elementType the type of the stream elements
 	 * @param sourceType the type to convert from
 	 */
-	public boolean matchesToStream(TypeDescriptor elementType, TypeDescriptor sourceType) {
+	public boolean matchesToStream(@Nullable TypeDescriptor elementType, TypeDescriptor sourceType) {
 		TypeDescriptor collectionOfElement = TypeDescriptor.collection(Collection.class, elementType);
 		return this.conversionService.canConvert(sourceType, collectionOfElement);
 	}
@@ -100,15 +101,19 @@ class StreamConverter implements ConditionalGenericConverter {
 		throw new IllegalStateException("Unexpected source/target types");
 	}
 
-	private Object convertFromStream(Stream<?> source, TypeDescriptor streamType, TypeDescriptor targetType) {
-		List<Object> content = source.collect(Collectors.<Object>toList());
+	@Nullable
+	private Object convertFromStream(@Nullable Stream<?> source, TypeDescriptor streamType, TypeDescriptor targetType) {
+		List<Object> content = (source != null ? source.collect(Collectors.<Object>toList()) : Collections.emptyList());
 		TypeDescriptor listType = TypeDescriptor.collection(List.class, streamType.getElementTypeDescriptor());
 		return this.conversionService.convert(content, listType, targetType);
 	}
 
-	private Object convertToStream(Object source, TypeDescriptor sourceType, TypeDescriptor streamType) {
+	private Object convertToStream(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor streamType) {
 		TypeDescriptor targetCollection = TypeDescriptor.collection(List.class, streamType.getElementTypeDescriptor());
 		List<?> target = (List<?>) this.conversionService.convert(source, sourceType, targetCollection);
+		if (target == null) {
+			target = Collections.emptyList();
+		}
 		return target.stream();
 	}
 

spring-core/src/main/java/org/springframework/core/convert/support/StringToArrayConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,7 @@ import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.convert.converter.ConditionalGenericConverter;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
@@ -31,16 +32,19 @@ import org.springframework.util.StringUtils;
  * Only matches if String.class can be converted to the target array element type.
  *
  * @author Keith Donald
+ * @author Juergen Hoeller
  * @since 3.0
  */
 final class StringToArrayConverter implements ConditionalGenericConverter {
 
 	private final ConversionService conversionService;
 
+
 	public StringToArrayConverter(ConversionService conversionService) {
 		this.conversionService = conversionService;
 	}
 
+
 	@Override
 	public Set<ConvertiblePair> getConvertibleTypes() {
 		return Collections.singleton(new ConvertiblePair(String.class, Object[].class));
@@ -48,7 +52,8 @@ final class StringToArrayConverter implements ConditionalGenericConverter {
 
 	@Override
 	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
-		return this.conversionService.canConvert(sourceType, targetType.getElementTypeDescriptor());
+		return ConversionUtils.canConvertElements(sourceType, targetType.getElementTypeDescriptor(),
+				this.conversionService);
 	}
 
 	@Override
@@ -59,10 +64,12 @@ final class StringToArrayConverter implements ConditionalGenericConverter {
 		}
 		String string = (String) source;
 		String[] fields = StringUtils.commaDelimitedListToStringArray(string);
-		Object target = Array.newInstance(targetType.getElementTypeDescriptor().getType(), fields.length);
+		TypeDescriptor targetElementType = targetType.getElementTypeDescriptor();
+		Assert.state(targetElementType != null, "No target element type");
+		Object target = Array.newInstance(targetElementType.getType(), fields.length);
 		for (int i = 0; i < fields.length; i++) {
 			String sourceElement = fields[i];
-			Object targetElement = this.conversionService.convert(sourceElement.trim(), sourceType, targetType.getElementTypeDescriptor());
+			Object targetElement = this.conversionService.convert(sourceElement.trim(), sourceType, targetElementType);
 			Array.set(target, i, targetElement);
 		}
 		return target;

spring-core/src/main/java/org/springframework/core/env/AbstractEnvironment.java

@@ -27,7 +27,6 @@ import org.apache.commons.logging.LogFactory;
 
 import org.springframework.core.SpringProperties;
 import org.springframework.core.convert.support.ConfigurableConversionService;
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
@@ -52,7 +51,6 @@ import org.springframework.util.StringUtils;
  * @see ConfigurableEnvironment
  * @see StandardEnvironment
  */
-@NonNullApi
 public abstract class AbstractEnvironment implements ConfigurableEnvironment {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/AbstractPropertyResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,7 +25,6 @@ import org.apache.commons.logging.LogFactory;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.support.ConfigurableConversionService;
 import org.springframework.core.convert.support.DefaultConversionService;
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -39,7 +38,6 @@ import org.springframework.util.SystemPropertyUtils;
  * @author Juergen Hoeller
  * @since 3.1
  */
-@NonNullApi
 public abstract class AbstractPropertyResolver implements ConfigurablePropertyResolver {
 
 	protected final Log logger = LogFactory.getLog(getClass());
@@ -131,10 +129,8 @@ public abstract class AbstractPropertyResolver implements ConfigurablePropertyRe
 
 	@Override
 	public void setRequiredProperties(String... requiredProperties) {
-		if (requiredProperties != null) {
-			for (String key : requiredProperties) {
-				this.requiredProperties.add(key);
-			}
+		for (String key : requiredProperties) {
+			this.requiredProperties.add(key);
 		}
 	}
 
@@ -247,7 +243,8 @@ public abstract class AbstractPropertyResolver implements ConfigurablePropertyRe
 	 * @since 4.3.5
 	 */
 	@SuppressWarnings("unchecked")
-	protected <T> T convertValueIfNecessary(Object value, Class<T> targetType) {
+	@Nullable
+	protected <T> T convertValueIfNecessary(Object value, @Nullable Class<T> targetType) {
 		if (targetType == null) {
 			return (T) value;
 		}

spring-core/src/main/java/org/springframework/core/env/CommandLineArgs.java

@@ -23,7 +23,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 
 /**
@@ -34,7 +33,6 @@ import org.springframework.lang.Nullable;
  * @since 3.1
  * @see SimpleCommandLineArgsParser
  */
-@NonNullApi
 class CommandLineArgs {
 
 	private final Map<String, List<String>> optionArgs = new HashMap<>();

spring-core/src/main/java/org/springframework/core/env/CommandLinePropertySource.java

@@ -19,7 +19,6 @@ package org.springframework.core.env;
 import java.util.Collection;
 import java.util.List;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 import org.springframework.util.StringUtils;
 
@@ -205,7 +204,6 @@ import org.springframework.util.StringUtils;
  * @see SimpleCommandLinePropertySource
  * @see JOptCommandLinePropertySource
  */
-@NonNullApi
 public abstract class CommandLinePropertySource<T> extends EnumerablePropertySource<T> {
 
 	/** The default name given to {@link CommandLinePropertySource} instances: {@value} */

spring-core/src/main/java/org/springframework/core/env/CompositePropertySource.java

@@ -23,7 +23,6 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.util.StringUtils;
 
 /**
@@ -40,7 +39,6 @@ import org.springframework.util.StringUtils;
  * @author Phillip Webb
  * @since 3.1.1
  */
-@NonNullApi
 public class CompositePropertySource extends EnumerablePropertySource<Object> {
 
 	private final Set<PropertySource<?>> propertySources = new LinkedHashSet<>();

spring-core/src/main/java/org/springframework/core/env/ConfigurableEnvironment.java

@@ -18,8 +18,6 @@ package org.springframework.core.env;
 
 import java.util.Map;
 
-import org.springframework.lang.NonNullApi;
-
 /**
  * Configuration interface to be implemented by most if not all {@link Environment} types.
  * Provides facilities for setting active and default profiles and manipulating underlying
@@ -71,7 +69,6 @@ import org.springframework.lang.NonNullApi;
  * @see StandardEnvironment
  * @see org.springframework.context.ConfigurableApplicationContext#getEnvironment
  */
-@NonNullApi
 public interface ConfigurableEnvironment extends Environment, ConfigurablePropertyResolver {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/ConfigurablePropertyResolver.java

@@ -17,7 +17,6 @@
 package org.springframework.core.env;
 
 import org.springframework.core.convert.support.ConfigurableConversionService;
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 
 /**
@@ -29,7 +28,6 @@ import org.springframework.lang.Nullable;
  * @author Chris Beams
  * @since 3.1
  */
-@NonNullApi
 public interface ConfigurablePropertyResolver extends PropertyResolver {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/EnumerablePropertySource.java

@@ -16,7 +16,6 @@
 
 package org.springframework.core.env;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.util.ObjectUtils;
 
 /**
@@ -42,7 +41,6 @@ import org.springframework.util.ObjectUtils;
  * @author Juergen Hoeller
  * @since 3.1
  */
-@NonNullApi
 public abstract class EnumerablePropertySource<T> extends PropertySource<T> {
 
 	public EnumerablePropertySource(String name, T source) {

spring-core/src/main/java/org/springframework/core/env/Environment.java

@@ -16,8 +16,6 @@
 
 package org.springframework.core.env;
 
-import org.springframework.lang.NonNullApi;
-
 /**
  * Interface representing the environment in which the current application is running.
  * Models two key aspects of the application environment: <em>profiles</em> and
@@ -70,7 +68,6 @@ import org.springframework.lang.NonNullApi;
  * @see org.springframework.context.ConfigurableApplicationContext#setEnvironment
  * @see org.springframework.context.support.AbstractApplicationContext#createEnvironment
  */
-@NonNullApi
 public interface Environment extends PropertyResolver {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/EnvironmentCapable.java

@@ -41,8 +41,7 @@ package org.springframework.core.env;
 public interface EnvironmentCapable {
 
 	/**
-	 * Return the {@link Environment} associated with this component
-	 * (may be {@code null} or a default environment).
+	 * Return the {@link Environment} associated with this component.
 	 */
 	Environment getEnvironment();
 

spring-core/src/main/java/org/springframework/core/env/JOptCommandLinePropertySource.java

@@ -23,8 +23,6 @@ import java.util.List;
 import joptsimple.OptionSet;
 import joptsimple.OptionSpec;
 
-import org.springframework.lang.NonNullApi;
-
 /**
  * {@link CommandLinePropertySource} implementation backed by a JOpt {@link OptionSet}.
  *
@@ -56,7 +54,6 @@ import org.springframework.lang.NonNullApi;
  * @see joptsimple.OptionParser
  * @see joptsimple.OptionSet
  */
-@NonNullApi
 public class JOptCommandLinePropertySource extends CommandLinePropertySource<OptionSet> {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/MapPropertySource.java

@@ -18,7 +18,6 @@ package org.springframework.core.env;
 
 import java.util.Map;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.util.StringUtils;
 
 /**
@@ -29,7 +28,6 @@ import org.springframework.util.StringUtils;
  * @since 3.1
  * @see PropertiesPropertySource
  */
-@NonNullApi
 public class MapPropertySource extends EnumerablePropertySource<Map<String, Object>> {
 
 	public MapPropertySource(String name, Map<String, Object> source) {

spring-core/src/main/java/org/springframework/core/env/MissingRequiredPropertiesException.java

@@ -19,8 +19,6 @@ package org.springframework.core.env;
 import java.util.LinkedHashSet;
 import java.util.Set;
 
-import org.springframework.lang.NonNullApi;
-
 /**
  * Exception thrown when required properties are not found.
  *
@@ -31,7 +29,6 @@ import org.springframework.lang.NonNullApi;
  * @see org.springframework.context.support.AbstractApplicationContext#prepareRefresh()
  */
 @SuppressWarnings("serial")
-@NonNullApi
 public class MissingRequiredPropertiesException extends IllegalStateException {
 
 	private final Set<String> missingRequiredProperties = new LinkedHashSet<>();

spring-core/src/main/java/org/springframework/core/env/MutablePropertySources.java

@@ -23,7 +23,6 @@ import java.util.concurrent.CopyOnWriteArrayList;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 import org.springframework.util.StringUtils;
 
@@ -41,7 +40,6 @@ import org.springframework.util.StringUtils;
  * @since 3.1
  * @see PropertySourcesPropertyResolver
  */
-@NonNullApi
 public class MutablePropertySources implements PropertySources {
 
 	private final Log logger;

spring-core/src/main/java/org/springframework/core/env/PropertiesPropertySource.java

@@ -19,8 +19,6 @@ package org.springframework.core.env;
 import java.util.Map;
 import java.util.Properties;
 
-import org.springframework.lang.NonNullApi;
-
 /**
  * {@link PropertySource} implementation that extracts properties from a
  * {@link java.util.Properties} object.
@@ -35,7 +33,6 @@ import org.springframework.lang.NonNullApi;
  * @author Juergen Hoeller
  * @since 3.1
  */
-@NonNullApi
 public class PropertiesPropertySource extends MapPropertySource {
 
 	@SuppressWarnings({"unchecked", "rawtypes"})

spring-core/src/main/java/org/springframework/core/env/PropertyResolver.java

@@ -16,7 +16,6 @@
 
 package org.springframework.core.env;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 
 /**
@@ -28,7 +27,6 @@ import org.springframework.lang.Nullable;
  * @see Environment
  * @see PropertySourcesPropertyResolver
  */
-@NonNullApi
 public interface PropertyResolver {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/PropertySource.java

@@ -19,7 +19,6 @@ package org.springframework.core.env;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
@@ -57,7 +56,6 @@ import org.springframework.util.ObjectUtils;
  * @see MutablePropertySources
  * @see org.springframework.context.annotation.PropertySource
  */
-@NonNullApi
 public abstract class PropertySource<T> {
 
 	protected final Log logger = LogFactory.getLog(getClass());

spring-core/src/main/java/org/springframework/core/env/PropertySources.java

@@ -16,7 +16,6 @@
 
 package org.springframework.core.env;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 
 /**
@@ -25,7 +24,6 @@ import org.springframework.lang.Nullable;
  * @author Chris Beams
  * @since 3.1
  */
-@NonNullApi
 public interface PropertySources extends Iterable<PropertySource<?>> {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/PropertySourcesPropertyResolver.java

@@ -16,7 +16,6 @@
 
 package org.springframework.core.env;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 
 /**
@@ -30,7 +29,6 @@ import org.springframework.lang.Nullable;
  * @see PropertySources
  * @see AbstractEnvironment
  */
-@NonNullApi
 public class PropertySourcesPropertyResolver extends AbstractPropertyResolver {
 
 	private final PropertySources propertySources;

spring-core/src/main/java/org/springframework/core/env/ReadOnlySystemAttributesMap.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,7 +21,7 @@ import java.util.Collections;
 import java.util.Map;
 import java.util.Set;
 
-import org.springframework.lang.NonNullApi;
+import org.springframework.lang.Nullable;
 
 /**
  * Read-only {@code Map<String, String>} implementation that is backed by system
@@ -37,7 +37,6 @@ import org.springframework.lang.NonNullApi;
  * @author Chris Beams
  * @since 3.0
  */
-@NonNullApi
 abstract class ReadOnlySystemAttributesMap implements Map<String, String> {
 
 	@Override
@@ -50,13 +49,13 @@ abstract class ReadOnlySystemAttributesMap implements Map<String, String> {
 	 * @throws IllegalArgumentException if given key is non-String
 	 */
 	@Override
+	@Nullable
 	public String get(Object key) {
 		if (!(key instanceof String)) {
 			throw new IllegalArgumentException(
-					"Type of key [" + (key != null ? key.getClass().getName() : "null") +
-					"] must be java.lang.String.");
+					"Type of key [" + key.getClass().getName() + "] must be java.lang.String");
 		}
-		return this.getSystemAttribute((String) key);
+		return getSystemAttribute((String) key);
 	}
 
 	@Override
@@ -68,6 +67,7 @@ abstract class ReadOnlySystemAttributesMap implements Map<String, String> {
 	 * Template method that returns the underlying system attribute.
 	 * <p>Implementations typically call {@link System#getProperty(String)} or {@link System#getenv(String)} here.
 	 */
+	@Nullable
 	protected abstract String getSystemAttribute(String attributeName);
 
 

spring-core/src/main/java/org/springframework/core/env/SimpleCommandLineArgsParser.java

@@ -16,8 +16,6 @@
 
 package org.springframework.core.env;
 
-import org.springframework.lang.NonNullApi;
-
 /**
  * Parses a {@code String[]} of command line arguments in order to populate a
  * {@link CommandLineArgs} object.
@@ -51,7 +49,6 @@ import org.springframework.lang.NonNullApi;
  * @author Chris Beams
  * @since 3.1
  */
-@NonNullApi
 class SimpleCommandLineArgsParser {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/SimpleCommandLinePropertySource.java

@@ -18,8 +18,6 @@ package org.springframework.core.env;
 
 import java.util.List;
 
-import org.springframework.lang.NonNullApi;
-
 /**
  * {@link CommandLinePropertySource} implementation backed by a simple String array.
  *
@@ -77,7 +75,6 @@ import org.springframework.lang.NonNullApi;
  * @see CommandLinePropertySource
  * @see JOptCommandLinePropertySource
  */
-@NonNullApi
 public class SimpleCommandLinePropertySource extends CommandLinePropertySource<CommandLineArgs> {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/StandardEnvironment.java

@@ -16,8 +16,6 @@
 
 package org.springframework.core.env;
 
-import org.springframework.lang.NonNullApi;
-
 /**
  * {@link Environment} implementation suitable for use in 'standard' (i.e. non-web)
  * applications.
@@ -53,7 +51,6 @@ import org.springframework.lang.NonNullApi;
  * @see SystemEnvironmentPropertySource
  * @see org.springframework.web.context.support.StandardServletEnvironment
  */
-@NonNullApi
 public class StandardEnvironment extends AbstractEnvironment {
 
 	/** System environment property source name: {@value} */

spring-core/src/main/java/org/springframework/core/env/SystemEnvironmentPropertySource.java

@@ -18,7 +18,6 @@ package org.springframework.core.env;
 
 import java.util.Map;
 
-import org.springframework.lang.NonNullApi;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -64,7 +63,6 @@ import org.springframework.util.Assert;
  * @see AbstractEnvironment#getSystemEnvironment()
  * @see AbstractEnvironment#ACTIVE_PROFILES_PROPERTY_NAME
  */
-@NonNullApi
 public class SystemEnvironmentPropertySource extends MapPropertySource {
 
 	/**

spring-core/src/main/java/org/springframework/core/env/package-info.java

@@ -2,4 +2,7 @@
  * Spring's environment abstraction consisting of bean definition
  * profile and hierarchical property source support.
  */
+@NonNullApi
 package org.springframework.core.env;
+
+import org.springframework.lang.NonNullApi;

spring-core/src/main/java/org/springframework/core/io/AbstractResource.java

@@ -144,7 +144,6 @@ public abstract class AbstractResource implements Resource {
 	@Override
 	public long contentLength() throws IOException {
 		InputStream is = getInputStream();
-		Assert.state(is != null, "Resource InputStream must not be null");
 		try {
 			long size = 0;
 			byte[] buf = new byte[255];

spring-core/src/main/java/org/springframework/core/io/ByteArrayResource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,9 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.util.Arrays;
 
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
 /**
  * {@link Resource} implementation for a given byte array.
  * <p>Creates a {@link ByteArrayInputStream} for the given byte array.
@@ -57,10 +60,8 @@ public class ByteArrayResource extends AbstractResource {
 	 * @param byteArray the byte array to wrap
 	 * @param description where the byte array comes from
 	 */
-	public ByteArrayResource(byte[] byteArray, String description) {
-		if (byteArray == null) {
-			throw new IllegalArgumentException("Byte array must not be null");
-		}
+	public ByteArrayResource(byte[] byteArray, @Nullable String description) {
+		Assert.notNull(byteArray, "Byte array must not be null");
 		this.byteArray = byteArray;
 		this.description = (description != null ? description : "");
 	}

spring-core/src/main/java/org/springframework/core/io/DefaultResourceLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -189,7 +189,7 @@ public class DefaultResourceLoader implements ResourceLoader {
 	 */
 	protected static class ClassPathContextResource extends ClassPathResource implements ContextResource {
 
-		public ClassPathContextResource(String path, ClassLoader classLoader) {
+		public ClassPathContextResource(String path, @Nullable ClassLoader classLoader) {
 			super(path, classLoader);
 		}
 

spring-core/src/main/java/org/springframework/core/io/DescriptiveResource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,8 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Simple {@link Resource} implementation that holds a resource description
  * but does not point to an actually readable resource.
@@ -39,7 +41,7 @@ public class DescriptiveResource extends AbstractResource {
 	 * Create a new DescriptiveResource.
 	 * @param description the resource description
 	 */
-	public DescriptiveResource(String description) {
+	public DescriptiveResource(@Nullable String description) {
 		this.description = (description != null ? description : "");
 	}
 

spring-core/src/main/java/org/springframework/core/io/FileSystemResourceLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,7 +48,7 @@ public class FileSystemResourceLoader extends DefaultResourceLoader {
 	 */
 	@Override
 	protected Resource getResourceByPath(String path) {
-		if (path != null && path.startsWith("/")) {
+		if (path.startsWith("/")) {
 			path = path.substring(1);
 		}
 		return new FileSystemContextResource(path);

spring-core/src/main/java/org/springframework/core/io/InputStreamResource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@ package org.springframework.core.io;
 import java.io.IOException;
 import java.io.InputStream;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -63,7 +64,7 @@ public class InputStreamResource extends AbstractResource {
 	 * @param inputStream the InputStream to use
 	 * @param description where the InputStream comes from
 	 */
-	public InputStreamResource(InputStream inputStream, String description) {
+	public InputStreamResource(InputStream inputStream, @Nullable String description) {
 		Assert.notNull(inputStream, "InputStream must not be null");
 		this.inputStream = inputStream;
 		this.description = (description != null ? description : "");

spring-core/src/main/java/org/springframework/core/io/ResourceEditor.java

@@ -70,7 +70,7 @@ public class ResourceEditor extends PropertyEditorSupport {
 	 * @param resourceLoader the {@code ResourceLoader} to use
 	 * @param propertyResolver the {@code PropertyResolver} to use
 	 */
-	public ResourceEditor(ResourceLoader resourceLoader, PropertyResolver propertyResolver) {
+	public ResourceEditor(ResourceLoader resourceLoader, @Nullable PropertyResolver propertyResolver) {
 		this(resourceLoader, propertyResolver, true);
 	}
 
@@ -82,7 +82,7 @@ public class ResourceEditor extends PropertyEditorSupport {
 	 * @param ignoreUnresolvablePlaceholders whether to ignore unresolvable placeholders
 	 * if no corresponding property could be found in the given {@code propertyResolver}
 	 */
-	public ResourceEditor(ResourceLoader resourceLoader, PropertyResolver propertyResolver,
+	public ResourceEditor(ResourceLoader resourceLoader, @Nullable PropertyResolver propertyResolver,
 			boolean ignoreUnresolvablePlaceholders) {
 
 		Assert.notNull(resourceLoader, "ResourceLoader must not be null");

spring-core/src/main/java/org/springframework/core/io/ResourceLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -71,8 +71,7 @@ public interface ResourceLoader {
 	 * <p>Clients which need to access the ClassLoader directly can do so
 	 * in a uniform manner with the ResourceLoader, rather than relying
 	 * on the thread context ClassLoader.
-	 * @return the ClassLoader (only {@code null} if even the system
-	 * ClassLoader isn't accessible)
+	 * @return the ClassLoader
 	 * @see org.springframework.util.ClassUtils#getDefaultClassLoader()
 	 */
 	@Nullable

spring-core/src/main/java/org/springframework/core/io/UrlResource.java

@@ -26,6 +26,7 @@ import java.net.URISyntaxException;
 import java.net.URL;
 import java.net.URLConnection;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ResourceUtils;
 import org.springframework.util.StringUtils;
@@ -121,7 +122,7 @@ public class UrlResource extends AbstractFileResolvingResource {
 	 * @throws MalformedURLException if the given URL specification is not valid
 	 * @see java.net.URI#URI(String, String, String)
 	 */
-	public UrlResource(String protocol, String location, String fragment) throws MalformedURLException  {
+	public UrlResource(String protocol, String location, @Nullable String fragment) throws MalformedURLException  {
 		try {
 			this.uri = new URI(protocol, location, fragment);
 			this.url = this.uri.toURL();

spring-core/src/main/java/org/springframework/core/io/VfsUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -183,10 +183,12 @@ public abstract class VfsUtils {
 		return invokeVfsMethod(VFS_METHOD_GET_ROOT_URL, null, url);
 	}
 
-	protected static Object doGetVisitorAttribute() {
+	@Nullable
+	protected static Object doGetVisitorAttributes() {
 		return ReflectionUtils.getField(VISITOR_ATTRIBUTES_FIELD_RECURSE, null);
 	}
 
+	@Nullable
 	protected static String doGetPath(Object resource) {
 		return (String) ReflectionUtils.invokeMethod(VIRTUAL_FILE_METHOD_GET_PATH_NAME, resource);
 	}

spring-core/src/main/java/org/springframework/core/io/buffer/DataBufferUtils.java

@@ -32,6 +32,7 @@ import reactor.core.publisher.Flux;
 import reactor.core.publisher.FluxSink;
 import reactor.core.publisher.SynchronousSink;
 
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -122,7 +123,7 @@ public abstract class DataBufferUtils {
 		});
 	}
 
-	private static void closeChannel(Channel channel) {
+	private static void closeChannel(@Nullable Channel channel) {
 		try {
 			if (channel != null) {
 				channel.close();

spring-core/src/main/java/org/springframework/core/io/support/DefaultPropertySourceFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@ package org.springframework.core.io.support;
 import java.io.IOException;
 
 import org.springframework.core.env.PropertySource;
+import org.springframework.lang.Nullable;
 
 /**
  * The default implementation for {@link PropertySourceFactory},
@@ -32,7 +33,7 @@ import org.springframework.core.env.PropertySource;
 public class DefaultPropertySourceFactory implements PropertySourceFactory {
 
 	@Override
-	public PropertySource<?> createPropertySource(String name, EncodedResource resource) throws IOException {
+	public PropertySource<?> createPropertySource(@Nullable String name, EncodedResource resource) throws IOException {
 		return (name != null ? new ResourcePropertySource(name, resource) : new ResourcePropertySource(resource));
 	}
 

spring-core/src/main/java/org/springframework/core/io/support/EncodedResource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -66,7 +66,7 @@ public class EncodedResource implements InputStreamSource {
 	 * @param resource the {@code Resource} to hold (never {@code null})
 	 * @param encoding the encoding to use for reading from the resource
 	 */
-	public EncodedResource(Resource resource, String encoding) {
+	public EncodedResource(Resource resource, @Nullable String encoding) {
 		this(resource, encoding, null);
 	}
 
@@ -76,11 +76,11 @@ public class EncodedResource implements InputStreamSource {
 	 * @param resource the {@code Resource} to hold (never {@code null})
 	 * @param charset the {@code Charset} to use for reading from the resource
 	 */
-	public EncodedResource(Resource resource, Charset charset) {
+	public EncodedResource(Resource resource, @Nullable Charset charset) {
 		this(resource, null, charset);
 	}
 
-	private EncodedResource(Resource resource, String encoding, Charset charset) {
+	private EncodedResource(Resource resource, @Nullable String encoding, @Nullable Charset charset) {
 		super();
 		Assert.notNull(resource, "Resource must not be null");
 		this.resource = resource;

spring-core/src/main/java/org/springframework/core/io/support/LocalizedResourceHelper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -63,7 +63,7 @@ public class LocalizedResourceHelper {
 	 * Set the separator to use inbetween file name parts.
 	 * Default is an underscore ("_").
 	 */
-	public void setSeparator(String separator) {
+	public void setSeparator(@Nullable String separator) {
 		this.separator = (separator != null ? separator : DEFAULT_SEPARATOR);
 	}
 

spring-core/src/main/java/org/springframework/core/io/support/PathMatchingResourcePatternResolver.java

@@ -363,7 +363,7 @@ public class PathMatchingResourcePatternResolver implements ResourcePatternResol
 	 * @param result the set of resources to add jar roots to
 	 * @since 4.1.1
 	 */
-	protected void addAllClassLoaderJarRoots(ClassLoader classLoader, Set<Resource> result) {
+	protected void addAllClassLoaderJarRoots(@Nullable ClassLoader classLoader, Set<Resource> result) {
 		if (classLoader instanceof URLClassLoader) {
 			try {
 				for (URL url : ((URLClassLoader) classLoader).getURLs()) {
@@ -462,18 +462,21 @@ public class PathMatchingResourcePatternResolver implements ResourcePatternResol
 		Set<Resource> result = new LinkedHashSet<>(16);
 		for (Resource rootDirResource : rootDirResources) {
 			rootDirResource = resolveRootDirResource(rootDirResource);
-			URL rootDirURL = rootDirResource.getURL();
+			URL rootDirUrl = rootDirResource.getURL();
 			if (equinoxResolveMethod != null) {
-				if (rootDirURL.getProtocol().startsWith("bundle")) {
-					rootDirURL = (URL) ReflectionUtils.invokeMethod(equinoxResolveMethod, null, rootDirURL);
-					rootDirResource = new UrlResource(rootDirURL);
+				if (rootDirUrl.getProtocol().startsWith("bundle")) {
+					URL resolvedUrl = (URL) ReflectionUtils.invokeMethod(equinoxResolveMethod, null, rootDirUrl);
+					if (resolvedUrl != null) {
+						rootDirUrl = resolvedUrl;
+					}
+					rootDirResource = new UrlResource(rootDirUrl);
 				}
 			}
-			if (rootDirURL.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
-				result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirURL, subPattern, getPathMatcher()));
+			if (rootDirUrl.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
+				result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirUrl, subPattern, getPathMatcher()));
 			}
-			else if (ResourceUtils.isJarURL(rootDirURL) || isJarResource(rootDirResource)) {
-				result.addAll(doFindPathMatchingJarResources(rootDirResource, rootDirURL, subPattern));
+			else if (ResourceUtils.isJarURL(rootDirUrl) || isJarResource(rootDirResource)) {
+				result.addAll(doFindPathMatchingJarResources(rootDirResource, rootDirUrl, subPattern));
 			}
 			else {
 				result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));
@@ -851,8 +854,9 @@ public class PathMatchingResourcePatternResolver implements ResourcePatternResol
 			}
 		}
 
+		@Nullable
 		public Object getAttributes() {
-			return VfsPatternUtils.getVisitorAttribute();
+			return VfsPatternUtils.getVisitorAttributes();
 		}
 
 		public Set<Resource> getResources() {