diff --git a/spring-test/src/main/java/org/springframework/test/util/AssertionErrors.java b/spring-test/src/main/java/org/springframework/test/util/AssertionErrors.java
index aea7f8e4cf..1865847673 100644
--- a/spring-test/src/main/java/org/springframework/test/util/AssertionErrors.java
+++ b/spring-test/src/main/java/org/springframework/test/util/AssertionErrors.java
@@ -76,9 +76,9 @@ public abstract class AssertionErrors {
 	 * {@link AssertionError} otherwise.
 	 * @param message a message that describes the reason for the failure
 	 * @param object the object to check
-	 * @since 5.1
+	 * @since 5.1.8
 	 */
-	public static void assertNotNull(String message, Object object) {
+	public static void assertNotNull(String message, @Nullable Object object) {
 		assertTrue(message, object != null);
 	}