Make getters and setters null-safety consistent

This commit ensure that null-safety is consistent between
getters and setters in order to be able to provide beans
with properties with a common type when type safety is
taken in account like with Kotlin.

It also add a few missing property level @Nullable
annotations.

Issue: SPR-15792

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

@@ -56,7 +56,7 @@ public class ConvertingPropertyEditorAdapter extends PropertyEditorSupport {
 
 
 	@Override
-	public void setAsText(String text) throws IllegalArgumentException {
+	public void setAsText(@Nullable String text) throws IllegalArgumentException {
 		setValue(this.conversionService.convert(text, TypeDescriptor.valueOf(String.class), this.targetDescriptor));
 	}
 

spring-core/src/main/java/org/springframework/core/task/SimpleAsyncTaskExecutor.java

@@ -103,7 +103,7 @@ public class SimpleAsyncTaskExecutor extends CustomizableThreadCreator implement
 	 * @see #setThreadNamePrefix
 	 * @see #setThreadPriority
 	 */
-	public void setThreadFactory(ThreadFactory threadFactory) {
+	public void setThreadFactory(@Nullable ThreadFactory threadFactory) {
 		this.threadFactory = threadFactory;
 	}
 

spring-core/src/main/java/org/springframework/util/CollectionUtils.java

@@ -430,7 +430,7 @@ public abstract class CollectionUtils {
 		}
 
 		@Override
-		public void set(K key, V value) {
+		public void set(K key, @Nullable V value) {
 			List<V> values = new LinkedList<>();
 			values.add(value);
 			this.map.put(key, values);

spring-core/src/main/java/org/springframework/util/CustomizableThreadCreator.java

@@ -127,7 +127,7 @@ public class CustomizableThreadCreator implements Serializable {
 	 * Specify the thread group that threads should be created in.
 	 * @see #setThreadGroupName
 	 */
-	public void setThreadGroup(ThreadGroup threadGroup) {
+	public void setThreadGroup(@Nullable ThreadGroup threadGroup) {
 		this.threadGroup = threadGroup;
 	}
 

spring-core/src/main/java/org/springframework/util/LinkedMultiValueMap.java

@@ -101,7 +101,7 @@ public class LinkedMultiValueMap<K, V> implements MultiValueMap<K, V>, Serializa
 	}
 
 	@Override
-	public void set(K key, V value) {
+	public void set(K key, @Nullable V value) {
 		List<V> values = new LinkedList<>();
 		values.add(value);
 		this.targetMap.put(key, values);

spring-core/src/main/java/org/springframework/util/MethodInvoker.java

@@ -65,7 +65,7 @@ public class MethodInvoker {
 	 * @see #setTargetObject
 	 * @see #setTargetMethod
 	 */
-	public void setTargetClass(Class<?> targetClass) {
+	public void setTargetClass(@Nullable Class<?> targetClass) {
 		this.targetClass = targetClass;
 	}
 
@@ -106,7 +106,7 @@ public class MethodInvoker {
 	 * @see #setTargetClass
 	 * @see #setTargetObject
 	 */
-	public void setTargetMethod(String targetMethod) {
+	public void setTargetMethod(@Nullable String targetMethod) {
 		this.targetMethod = targetMethod;
 	}
 

spring-core/src/main/java/org/springframework/util/MultiValueMap.java

@@ -64,7 +64,7 @@ public interface MultiValueMap<K, V> extends Map<K, List<V>> {
 	 * @param key the key
 	 * @param value the value to set
 	 */
-	void set(K key, V value);
+	void set(K key, @Nullable V value);
 
 	/**
 	 * Set the given values under.

spring-core/src/main/java/org/springframework/util/xml/AbstractXMLReader.java

@@ -41,19 +41,24 @@ import org.springframework.lang.Nullable;
  */
 abstract class AbstractXMLReader implements XMLReader {
 
+	@Nullable
 	private DTDHandler dtdHandler;
 
+	@Nullable
 	private ContentHandler contentHandler;
 
+	@Nullable
 	private EntityResolver entityResolver;
 
+	@Nullable
 	private ErrorHandler errorHandler;
 
+	@Nullable
 	private LexicalHandler lexicalHandler;
 
 
 	@Override
-	public void setContentHandler(ContentHandler contentHandler) {
+	public void setContentHandler(@Nullable ContentHandler contentHandler) {
 		this.contentHandler = contentHandler;
 	}
 
@@ -64,7 +69,7 @@ abstract class AbstractXMLReader implements XMLReader {
 	}
 
 	@Override
-	public void setDTDHandler(DTDHandler dtdHandler) {
+	public void setDTDHandler(@Nullable DTDHandler dtdHandler) {
 		this.dtdHandler = dtdHandler;
 	}
 
@@ -75,7 +80,7 @@ abstract class AbstractXMLReader implements XMLReader {
 	}
 
 	@Override
-	public void setEntityResolver(EntityResolver entityResolver) {
+	public void setEntityResolver(@Nullable EntityResolver entityResolver) {
 		this.entityResolver = entityResolver;
 	}
 
@@ -86,7 +91,7 @@ abstract class AbstractXMLReader implements XMLReader {
 	}
 
 	@Override
-	public void setErrorHandler(ErrorHandler errorHandler) {
+	public void setErrorHandler(@Nullable ErrorHandler errorHandler) {
 		this.errorHandler = errorHandler;
 	}