ConcurrentModel.addAttribute javadoc: null value not supported

Issue: SPR-16831

spring-context/src/main/java/org/springframework/ui/ConcurrentModel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -68,7 +68,8 @@ public class ConcurrentModel extends ConcurrentHashMap<String, Object> implement
 	/**
 	 * Add the supplied attribute under the supplied name.
 	 * @param attributeName the name of the model attribute (never {@code null})
-	 * @param attributeValue the model attribute value (can be {@code null})
+	 * @param attributeValue the model attribute value (never {@code null} for {@code ConcurrentModel},
+	 * with the {@code Nullable} declaration inherited from {@link Model#addAttribute(String, Object)})
 	 */
 	public ConcurrentModel addAttribute(String attributeName, @Nullable Object attributeValue) {
 		Assert.notNull(attributeName, "Model attribute name must not be null");
@@ -80,14 +81,14 @@ public class ConcurrentModel extends ConcurrentHashMap<String, Object> implement
 	/**
 	 * Add the supplied attribute to this {@code Map} using a
 	 * {@link org.springframework.core.Conventions#getVariableName generated name}.
-	 * <p><emphasis>Note: Empty {@link Collection Collections} are not added to
+	 * <p><i>Note: Empty {@link Collection Collections} are not added to
 	 * the model when using this method because we cannot correctly determine
 	 * the true convention name. View code should check for {@code null} rather
-	 * than for empty collections as is already done by JSTL tags.</emphasis>
+	 * than for empty collections as is already done by JSTL tags.</i>
 	 * @param attributeValue the model attribute value (never {@code null})
 	 */
-	public ConcurrentModel addAttribute(@Nullable Object attributeValue) {
-		Assert.notNull(attributeValue, "Model object must not be null");
+	public ConcurrentModel addAttribute(Object attributeValue) {
+		Assert.notNull(attributeValue, "Model attribute value must not be null");
 		if (attributeValue instanceof Collection && ((Collection<?>) attributeValue).isEmpty()) {
 			return this;
 		}