#53 - Tightened nullability contract and added nullability annotations.

core/src/main/java/org/springframework/plugin/core/OrderAwarePluginRegistry.java

@@ -86,7 +86,7 @@ public class OrderAwarePluginRegistry<T extends Plugin<S>, S> extends SimplePlug
 
 		Assert.notNull(comparator, "Comparator must not be null!");
 
-		return create(Collections.emptyList(), comparator);
+		return of(Collections.emptyList(), comparator);
 	}
 
 	/**
@@ -98,7 +98,7 @@ public class OrderAwarePluginRegistry<T extends Plugin<S>, S> extends SimplePlug
 	 */
 	@SafeVarargs
 	public static <S, T extends Plugin<S>> OrderAwarePluginRegistry<T, S> of(T... plugins) {
-		return create(Arrays.asList(plugins), DEFAULT_COMPARATOR);
+		return of(Arrays.asList(plugins), DEFAULT_COMPARATOR);
 	}
 
 	/**
@@ -109,7 +109,7 @@ public class OrderAwarePluginRegistry<T extends Plugin<S>, S> extends SimplePlug
 	 * @since 2.0
 	 */
 	public static <S, T extends Plugin<S>> OrderAwarePluginRegistry<T, S> of(List<? extends T> plugins) {
-		return create(plugins, DEFAULT_COMPARATOR);
+		return of(plugins, DEFAULT_COMPARATOR);
 	}
 
 	/**
@@ -121,7 +121,7 @@ public class OrderAwarePluginRegistry<T extends Plugin<S>, S> extends SimplePlug
 	 * @since 2.0
 	 */
 	public static <S, T extends Plugin<S>> OrderAwarePluginRegistry<T, S> ofReverse(List<? extends T> plugins) {
-		return create(plugins, DEFAULT_REVERSE_COMPARATOR);
+		return of(plugins, DEFAULT_REVERSE_COMPARATOR);
 	}
 
 	/**
@@ -226,6 +226,6 @@ public class OrderAwarePluginRegistry<T extends Plugin<S>, S> extends SimplePlug
 	public OrderAwarePluginRegistry<T, S> reverse() {
 
 		List<T> copy = new ArrayList<>(getPlugins());
-		return create(copy, comparator.reversed());
+		return of(copy, comparator.reversed());
 	}
 }

core/src/main/java/org/springframework/plugin/core/Plugin.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2012 the original author or authors.
+ * Copyright 2008-2019 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.
@@ -20,15 +20,15 @@ package org.springframework.plugin.core;
  * Its core responsibility is to define a delimiter type and a selection callback with the delimiter as parameter. The
  * delimiter is some kind of decision object concrete plugin implementations can use to decide if they are capable to be
  * executed.
- * 
+ *
  * @author Oliver Gierke
  */
 public interface Plugin<S> {
 
 	/**
 	 * Returns if a plugin should be invoked according to the given delimiter.
-	 * 
-	 * @param delimiter
+	 *
+	 * @param delimiter must not be {@literal null}.
 	 * @return if the plugin should be invoked
 	 */
 	boolean supports(S delimiter);

core/src/main/java/org/springframework/plugin/core/PluginRegistry.java

@@ -101,7 +101,7 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	 * Returns the first {@link Plugin} found for the given delimiter. Thus, further configured {@link Plugin}s are
 	 * ignored.
 	 *
-	 * @param delimiter
+	 * @param delimiter must not be {@literal null}.
 	 * @return a plugin for the given delimiter or {@link Optional#empty()} if none found.
 	 */
 	Optional<T> getPluginFor(S delimiter);
@@ -110,7 +110,7 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	 * Returns the first {@link Plugin} found for the given delimiter. Thus, further configured {@link Plugin}s are
 	 * ignored.
 	 *
-	 * @param delimiter
+	 * @param delimiter must not be {@literal null}.
 	 * @return a {@link Plugin} for the given originating system or {@link Optional#empty()} if none found.
 	 * @throws IllegalArgumentException in case no {@link Plugin} for the given delimiter
 	 */
@@ -120,7 +120,7 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	 * Returns the first {@link Plugin} found for the given delimiter. Thus, further configured {@link Plugin}s are
 	 * ignored.
 	 *
-	 * @param delimiter
+	 * @param delimiter must not be {@literal null}.
 	 * @param message a {@link Supplier} to produce an exception message in case no plugin is found.
 	 * @return a {@link Plugin} for the given originating system or {@link Optional#empty()} if none found.
 	 * @throws IllegalArgumentException in case no {@link Plugin} for the given delimiter
@@ -130,7 +130,7 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	/**
 	 * Returns all plugins for the given delimiter.
 	 *
-	 * @param delimiter
+	 * @param delimiter must not be {@literal null}.
 	 * @return a list of plugins or an empty list if none found
 	 */
 	List<T> getPluginsFor(S delimiter);
@@ -140,8 +140,9 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	 * plugins are found the first one will be returned.
 	 *
 	 * @param <E> the exception type to be thrown in case no plugin can be found.
-	 * @param delimiter
-	 * @param ex a lazy {@link Supplier} to produce an exception in case no plugin can be found.
+	 * @param delimiter must not be {@literal null}.
+	 * @param ex a lazy {@link Supplier} to produce an exception in case no plugin can be found, must not be
+	 *          {@literal null}.
 	 * @return a single plugin for the given delimiter
 	 * @throws E if no plugin can be found for the given delimiter
 	 */
@@ -151,8 +152,9 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	 * Retrieves all plugins for the given delimiter or throws an exception if no plugin can be found.
 	 *
 	 * @param <E> the exception type to be thrown.
-	 * @param delimiter
-	 * @param ex a lazy {@link Supplier} to produce an exception in case no plugin can be found.
+	 * @param delimiter must not be {@literal null}.
+	 * @param ex a lazy {@link Supplier} to produce an exception in case no plugin can be found, must not be
+	 *          {@literal null}.
 	 * @return all plugins for the given delimiter
 	 * @throws E if no plugin can be found
 	 */
@@ -161,8 +163,8 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	/**
 	 * Returns the first {@link Plugin} supporting the given delimiter or the given plugin if none can be found.
 	 *
-	 * @param delimiter
-	 * @param plugin
+	 * @param delimiter must not be {@literal null}.
+	 * @param plugin must not be {@literal null}.
 	 * @return a single {@link Plugin} supporting the given delimiter or the given {@link Plugin} if none found
 	 */
 	T getPluginOrDefaultFor(S delimiter, T plugin);
@@ -181,9 +183,10 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	/**
 	 * Returns all {@link Plugin}s supporting the given delimiter or the given plugins if none found.
 	 *
-	 * @param delimiter
-	 * @param plugins
-	 * @return all {@link Plugin}s supporting the given delimiter or the given {@link Plugin}s if none found
+	 * @param delimiter must not be {@literal null}.
+	 * @param plugins must not be {@literal null}.
+	 * @return all {@link Plugin}s supporting the given delimiter or the given {@link Plugin}s if none found, will never
+	 *         be {@literal null}.
 	 */
 	List<T> getPluginsFor(S delimiter, List<? extends T> plugins);
 
@@ -197,7 +200,7 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	/**
 	 * Returns whether the registry contains a given plugin.
 	 *
-	 * @param plugin
+	 * @param plugin must not be {@literal null}.
 	 * @return
 	 */
 	boolean contains(T plugin);
@@ -205,7 +208,7 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	/**
 	 * Returns whether the registry contains a {@link Plugin} matching the given delimiter.
 	 *
-	 * @param delimiter
+	 * @param delimiter must not be {@literal null}.
 	 * @return
 	 */
 	boolean hasPluginFor(S delimiter);
@@ -214,7 +217,7 @@ public interface PluginRegistry<T extends Plugin<S>, S> extends Iterable<T> {
 	 * Returns all {@link Plugin}s contained in this registry. Will return an immutable {@link List} to prevent outside
 	 * modifications of the {@link PluginRegistry} content.
 	 *
-	 * @return
+	 * @return will never be {@literal null}.
 	 */
 	List<T> getPlugins();
 }

core/src/main/java/org/springframework/plugin/core/PluginRegistrySupport.java

@@ -18,6 +18,7 @@ package org.springframework.plugin.core;
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
+import java.util.stream.Collectors;
 
 import org.springframework.util.Assert;
 
@@ -73,15 +74,10 @@ public abstract class PluginRegistrySupport<T extends Plugin<S>, S> implements P
 	protected synchronized List<T> initialize(List<T> plugins) {
 
 		Assert.notNull(plugins, "Plugins must not be null!");
-		List<T> result = new ArrayList<T>();
 
-		for (T plugin : this.plugins) {
-			if (plugin != null) {
-				result.add(plugin);
-			}
-		}
-
-		return result;
+		return plugins.stream() //
+				.filter(it -> it != null) //
+				.collect(Collectors.toList());
 	}
 
 	/* 

core/src/main/java/org/springframework/plugin/core/SimplePluginRegistry.java

@@ -78,7 +78,7 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	 */
 	@Deprecated
 	public static <S, T extends Plugin<S>> SimplePluginRegistry<T, S> create() {
-		return create(Collections.<T> emptyList());
+		return of(Collections.<T> emptyList());
 	}
 
 	/**
@@ -107,6 +107,8 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	@Override
 	public Optional<T> getPluginFor(S delimiter) {
 
+		Assert.notNull(delimiter, "Delimiter must not be null!");
+
 		return super.getPlugins().stream()//
 				.filter(it -> it.supports(delimiter))//
 				.findFirst();
@@ -119,6 +121,8 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	@Override
 	public T getRequiredPluginFor(S delimiter) {
 
+		Assert.notNull(delimiter, "Delimiter must not be null!");
+
 		return getRequiredPluginFor(delimiter,
 				() -> String.format("No plugin found for delimiter %s! Registered plugins: %s.", delimiter, getPlugins()));
 	}
@@ -130,6 +134,7 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	@Override
 	public T getRequiredPluginFor(S delimiter, Supplier<String> message) throws IllegalArgumentException {
 
+		Assert.notNull(delimiter, "Delimiter must not be null!");
 		Assert.notNull(message, "Message must not be null!");
 
 		return getPluginFor(delimiter, () -> new IllegalArgumentException(message.get()));
@@ -142,6 +147,8 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	@Override
 	public List<T> getPluginsFor(S delimiter) {
 
+		Assert.notNull(delimiter, "Delimiter must not be null!");
+
 		return super.getPlugins().stream()//
 				.filter(it -> it.supports(delimiter))//
 				.collect(Collectors.toList());
@@ -153,6 +160,10 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	 */
 	@Override
 	public <E extends Exception> T getPluginFor(S delimiter, Supplier<E> ex) throws E {
+
+		Assert.notNull(delimiter, "Delimiter must not be null!");
+		Assert.notNull(ex, "Exception supplier must not be null!");
+
 		return getPluginFor(delimiter).orElseThrow(ex);
 	}
 
@@ -163,6 +174,9 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	@Override
 	public <E extends Exception> List<T> getPluginsFor(S delimiter, Supplier<E> ex) throws E {
 
+		Assert.notNull(delimiter, "Delimiter must not be null!");
+		Assert.notNull(ex, "Exception supplier must not be null!");
+
 		List<T> result = getPluginsFor(delimiter);
 
 		if (result.isEmpty()) {
@@ -187,6 +201,10 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	 */
 	@Override
 	public T getPluginOrDefaultFor(S delimiter, Supplier<T> defaultSupplier) {
+
+		Assert.notNull(delimiter, "Delimiter must not be null!");
+		Assert.notNull(defaultSupplier, "Default supplier must not be null!");
+
 		return getPluginFor(delimiter).orElseGet(defaultSupplier);
 	}
 
@@ -197,6 +215,9 @@ public class SimplePluginRegistry<T extends Plugin<S>, S> extends PluginRegistry
 	@Override
 	public List<T> getPluginsFor(S delimiter, List<? extends T> plugins) {
 
+		Assert.notNull(delimiter, "Delimiter must not be null!");
+		Assert.notNull(plugins, "Plugins must not be null!");
+
 		List<T> candidates = getPluginsFor(delimiter);
 
 		return candidates.isEmpty() ? new ArrayList<T>(plugins) : candidates;

core/src/main/java/org/springframework/plugin/core/config/PluginRegistriesBeanDefinitionRegistrar.java

@@ -15,6 +15,10 @@
  */
 package org.springframework.plugin.core.config;
 
+import java.util.Map;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.beans.factory.support.AutowireCandidateQualifier;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
@@ -39,15 +43,24 @@ import org.springframework.util.StringUtils;
  */
 public class PluginRegistriesBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
 
-	/* 
+	private static final Logger LOG = LoggerFactory.getLogger(PluginRegistriesBeanDefinitionRegistrar.class);
+
+	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.context.annotation.ImportBeanDefinitionRegistrar#registerBeanDefinitions(org.springframework.core.type.AnnotationMetadata, org.springframework.beans.factory.support.BeanDefinitionRegistry)
 	 */
 	@Override
 	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
 
-		Class<?>[] types = (Class<?>[]) importingClassMetadata
-				.getAnnotationAttributes(EnablePluginRegistries.class.getName()).get("value");
+		Map<String, Object> annotationAttributes = importingClassMetadata
+				.getAnnotationAttributes(EnablePluginRegistries.class.getName());
+
+		if (annotationAttributes == null) {
+			LOG.info("No EnablePluginRegistries annotation found on type {}!", importingClassMetadata.getClassName());
+			return;
+		}
+
+		Class<?>[] types = (Class<?>[]) annotationAttributes.get("value");
 
 		for (Class<?> type : types) {
 
@@ -67,8 +80,10 @@ public class PluginRegistriesBeanDefinitionRegistrar implements ImportBeanDefini
 			}
 
 			// Default
-			String beanName = annotation == null ? StringUtils.uncapitalize(type.getSimpleName() + "Registry")
+			String beanName = annotation == null //
+					? StringUtils.uncapitalize(type.getSimpleName() + "Registry") //
 					: annotation.value();
+
 			registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
 		}
 	}

core/src/main/java/org/springframework/plugin/core/package-info.java

@@ -1,5 +1,6 @@
 /**
- * This package contains the core plugin API. It allows other modules implementing components that extend functionality defined by a plugin interface. Plugin clients can be equipped with plugin implementations. 
+ * This package contains the core plugin API. It allows other modules implementing components that extend functionality
+ * defined by a plugin interface. Plugin clients can be equipped with plugin implementations.
  */
+@org.springframework.lang.NonNullApi
 package org.springframework.plugin.core;
-

core/src/main/java/org/springframework/plugin/core/support/AbstractTypeAwareSupport.java

@@ -20,6 +20,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
+import java.util.stream.Collectors;
 
 import org.springframework.aop.TargetSource;
 import org.springframework.aop.framework.ProxyFactory;
@@ -30,6 +31,8 @@ import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.event.ContextRefreshedEvent;
+import org.springframework.lang.NonNull;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -41,10 +44,10 @@ import org.springframework.util.Assert;
 public abstract class AbstractTypeAwareSupport<T>
 		implements ApplicationContextAware, ApplicationListener<ContextRefreshedEvent>, InitializingBean {
 
-	private ApplicationContext context;
-	private Class<T> type;
-	private BeansOfTypeTargetSource targetSource;
-	private Collection<Class<?>> exclusions;
+	private @Nullable ApplicationContext context;
+	private @Nullable Class<T> type;
+	private @Nullable BeansOfTypeTargetSource targetSource;
+	private Collection<Class<?>> exclusions = Collections.emptySet();
 
 	/*
 	 * (non-Javadoc)
@@ -80,7 +83,14 @@ public abstract class AbstractTypeAwareSupport<T>
 	@SuppressWarnings("unchecked")
 	protected List<T> getBeans() {
 
+		TargetSource targetSource = this.targetSource;
+
+		if (targetSource == null) {
+			throw new IllegalStateException("Traget source not initialized!");
+		}
+
 		ProxyFactory factory = new ProxyFactory(List.class, targetSource);
+
 		return (List<T>) factory.getProxy();
 	}
 
@@ -89,6 +99,19 @@ public abstract class AbstractTypeAwareSupport<T>
 	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet()
 	 */
 	public void afterPropertiesSet() {
+
+		ApplicationContext context = this.context;
+
+		if (context == null) {
+			throw new IllegalStateException("ApplicationContext not set!");
+		}
+
+		Class<?> type = this.type;
+
+		if (type == null) {
+			throw new IllegalStateException("No type configured!");
+		}
+
 		this.targetSource = new BeansOfTypeTargetSource(context, type, false, exclusions);
 	}
 
@@ -98,7 +121,7 @@ public abstract class AbstractTypeAwareSupport<T>
 	 */
 	public void onApplicationEvent(ContextRefreshedEvent event) {
 
-		if (context.equals(event.getApplicationContext())) {
+		if (event.getApplicationContext().equals(context) && targetSource != null) {
 			targetSource.freeze();
 		}
 	}
@@ -119,7 +142,7 @@ public abstract class AbstractTypeAwareSupport<T>
 		private final Collection<Class<?>> exclusions;
 
 		private boolean frozen = false;
-		private Collection<Object> components;
+		private @Nullable Collection<Object> components;
 
 		/**
 		 * Creates a new {@link BeansOfTypeTargetSource} using the given {@link ListableBeanFactory} to lookup beans of the
@@ -134,11 +157,13 @@ public abstract class AbstractTypeAwareSupport<T>
 
 			Assert.notNull(context, "ListableBeanFactory must not be null!");
 			Assert.notNull(type, "Type must not be null!");
+			Assert.notNull(exclusions, "Exclusions must not be null!");
 
 			this.context = context;
 			this.type = type;
 			this.eagerInit = eagerInit;
-			this.exclusions = exclusions == null ? Collections.<Class<?>> emptySet() : exclusions;
+			this.exclusions = exclusions;
+			this.components = null;
 		}
 
 		/**
@@ -153,6 +178,7 @@ public abstract class AbstractTypeAwareSupport<T>
 		 * (non-Javadoc)
 		 * @see org.springframework.aop.TargetSource#getTargetClass()
 		 */
+		@NonNull
 		public Class<?> getTargetClass() {
 			return List.class;
 		}
@@ -169,10 +195,12 @@ public abstract class AbstractTypeAwareSupport<T>
 		 * (non-Javadoc)
 		 * @see org.springframework.aop.TargetSource#getTarget()
 		 */
+		@NonNull
 		@SuppressWarnings({ "rawtypes", "unchecked" })
 		public synchronized Object getTarget() throws Exception {
 
-			Collection<Object> components = this.components == null ? getBeansOfTypeExcept(type, exclusions)
+			Collection<Object> components = this.components == null //
+					? getBeansOfTypeExcept(type, exclusions) //
 					: this.components;
 
 			if (frozen && this.components == null) {
@@ -186,22 +214,14 @@ public abstract class AbstractTypeAwareSupport<T>
 		 * (non-Javadoc)
 		 * @see org.springframework.aop.TargetSource#releaseTarget(java.lang.Object)
 		 */
-		public void releaseTarget(Object target) throws Exception {
-
-		}
+		public void releaseTarget(Object target) throws Exception {}
 
 		private Collection<Object> getBeansOfTypeExcept(Class<?> type, Collection<Class<?>> exceptions) {
 
-			List<Object> result = new ArrayList<Object>();
-
-			for (String beanName : context.getBeanNamesForType(type, false, eagerInit)) {
-				if (exceptions.contains(context.getType(beanName))) {
-					continue;
-				}
-				result.add(context.getBean(beanName));
-			}
-
-			return result;
+			return Arrays.stream(context.getBeanNamesForType(type, false, eagerInit)) //
+					.filter(it -> !exceptions.contains(context.getType(it))) //
+					.map(it -> context.getBean(it)) //
+					.collect(Collectors.toList());
 		}
 	}
 }

core/src/main/java/org/springframework/plugin/core/support/BeanListFactoryBean.java

@@ -22,6 +22,7 @@ import java.util.List;
 
 import org.springframework.beans.factory.FactoryBean;
 import org.springframework.core.annotation.AnnotationAwareOrderComparator;
+import org.springframework.lang.NonNull;
 
 /**
  * Factory to create bean lists for a given type. Exposes all beans of the configured type that can be found in the
@@ -37,6 +38,7 @@ public class BeanListFactoryBean<T> extends AbstractTypeAwareSupport<T> implemen
 	 * (non-Javadoc)
 	 * @see org.springframework.beans.factory.FactoryBean#getObject()
 	 */
+	@NonNull
 	public List<T> getObject() {
 
 		List<T> beans = new ArrayList<T>();
@@ -50,6 +52,7 @@ public class BeanListFactoryBean<T> extends AbstractTypeAwareSupport<T> implemen
 	 * (non-Javadoc)
 	 * @see org.springframework.beans.factory.FactoryBean#getObjectType()
 	 */
+	@NonNull
 	public Class<?> getObjectType() {
 		return List.class;
 	}

core/src/main/java/org/springframework/plugin/core/support/PluginRegistryFactoryBean.java

@@ -16,6 +16,7 @@
 package org.springframework.plugin.core.support;
 
 import org.springframework.beans.factory.FactoryBean;
+import org.springframework.lang.NonNull;
 import org.springframework.plugin.core.OrderAwarePluginRegistry;
 import org.springframework.plugin.core.Plugin;
 import org.springframework.plugin.core.PluginRegistry;
@@ -32,6 +33,7 @@ public class PluginRegistryFactoryBean<T extends Plugin<S>, S> extends AbstractT
 	 * (non-Javadoc)
 	 * @see org.springframework.beans.factory.FactoryBean#getObject()
 	 */
+	@NonNull
 	public OrderAwarePluginRegistry<T, S> getObject() {
 		return OrderAwarePluginRegistry.of(getBeans());
 	}
@@ -40,6 +42,7 @@ public class PluginRegistryFactoryBean<T extends Plugin<S>, S> extends AbstractT
 	 * (non-Javadoc)
 	 * @see org.springframework.beans.factory.FactoryBean#getObjectType()
 	 */
+	@NonNull
 	public Class<?> getObjectType() {
 		return OrderAwarePluginRegistry.class;
 	}

core/src/main/java/org/springframework/plugin/core/support/package-info.java

@@ -1,5 +1,6 @@
 /**
- * This package contains support classes to create bean lists or plugin registry instances out of beans implementing a certain interface.
+ * This package contains support classes to create bean lists or plugin registry instances out of beans implementing a
+ * certain interface.
  */
+@org.springframework.lang.NonNullApi
 package org.springframework.plugin.core.support;
-

core/src/test/java/org/springframework/plugin/core/OrderAwarePluginRegistryUnitTest.java

@@ -100,7 +100,7 @@ public class OrderAwarePluginRegistryUnitTest extends SimplePluginRegistryUnitTe
 
 	private static void assertOrder(PluginRegistry<TestPlugin, String> registry, TestPlugin... plugins) {
 
-		List<TestPlugin> result = registry.getPluginsFor(null);
+		List<TestPlugin> result = registry.getPluginsFor("delimiter");
 
 		assertThat(plugins.length, is(result.size()));
 
@@ -108,7 +108,7 @@ public class OrderAwarePluginRegistryUnitTest extends SimplePluginRegistryUnitTe
 			assertThat(result.get(i), is(plugins[i]));
 		}
 
-		assertThat(registry.getPluginFor(null), is(Optional.of(plugins[0])));
+		assertThat(registry.getPluginFor("delimiter"), is(Optional.of(plugins[0])));
 	}
 
 	private static void assertDefaultComparator(OrderAwarePluginRegistry<?, ?> registry) {