ResolvableType.forInstance returns NONE for null instance

Closes gh-28776

Author: jhoeller

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

@@ -221,9 +221,8 @@ public Class<?> getRawClass() {
 	/**
 	 * Return the underlying source of the resolvable type. Will return a {@link Field},
 	 * {@link MethodParameter} or {@link Type} depending on how the {@link ResolvableType}
-	 * was constructed. With the exception of the {@link #NONE} constant, this method will
-	 * never return {@code null}. This method is primarily to provide access to additional
-	 * type information or meta-data that alternative JVM languages may provide.
+	 * was constructed. This method is primarily to provide access to additional type
+	 * information or meta-data that alternative JVM languages may provide.
 	 */
 	public Object getSource() {
 		Object source = (this.typeProvider != null ? this.typeProvider.getSource() : null);
@@ -1103,20 +1102,20 @@ public static ResolvableType forClassWithGenerics(Class<?> clazz, ResolvableType
 	 * convey generic information but if it implements {@link ResolvableTypeProvider} a
 	 * more precise {@link ResolvableType} can be used than the simple one based on
 	 * the {@link #forClass(Class) Class instance}.
-	 * @param instance the instance
-	 * @return a {@link ResolvableType} for the specified instance
+	 * @param instance the instance (possibly {@code null})
+	 * @return a {@link ResolvableType} for the specified instance,
+	 * or {@code NONE} for {@code null}
 	 * @since 4.2
 	 * @see ResolvableTypeProvider
 	 */
-	public static ResolvableType forInstance(Object instance) {
-		Assert.notNull(instance, "Instance must not be null");
+	public static ResolvableType forInstance(@Nullable Object instance) {
 		if (instance instanceof ResolvableTypeProvider) {
 			ResolvableType type = ((ResolvableTypeProvider) instance).getResolvableType();
 			if (type != null) {
 				return type;
 			}
 		}
-		return ResolvableType.forClass(instance.getClass());
+		return (instance != null ? forClass(instance.getClass()) : NONE);
 	}
 
 	/**

spring-core/src/test/java/org/springframework/core/ResolvableTypeTests.java

@@ -146,11 +146,9 @@ void forRawClassAssignableFromTypeVariable() throws Exception {
 		assertThat(typeVariable.isAssignableFrom(raw)).isTrue();
 	}
 
-	@Test
-	void forInstanceMustNotBeNull() throws Exception {
-		assertThatIllegalArgumentException()
-			.isThrownBy(() -> ResolvableType.forInstance(null))
-			.withMessage("Instance must not be null");
+	@Test  // gh-28776
+	void forInstanceNull() throws Exception {
+		assertThat(ResolvableType.forInstance(null)).isEqualTo(ResolvableType.NONE);
 	}
 
 	@Test