Consistently declare Object::equals argument as @Nullable

spring-expression/src/test/java/org/springframework/expression/spel/SpelReproTests.java

@@ -2251,7 +2251,7 @@ class SpelReproTests extends AbstractExpressionTests {
 		}
 
 		@Override
-		public boolean equals(Object other) {
+		public boolean equals(@Nullable Object other) {
 			return (this == other || (other instanceof TestClass2 &&
 					this.string.equals(((TestClass2) other).string)));
 		}

spring-expression/src/test/java/org/springframework/expression/spel/testresources/PlaceOfBirth.java

@@ -16,6 +16,8 @@
 
 package org.springframework.expression.spel.testresources;
 
+import org.springframework.lang.Nullable;
+
 ///CLOVER:OFF
 public class PlaceOfBirth {
 
@@ -51,7 +53,7 @@ public class PlaceOfBirth {
 	}
 
 	@Override
-	public boolean equals(Object o) {
+	public boolean equals(@Nullable Object o) {
 		if (!(o instanceof PlaceOfBirth otherPOB)) {
 			return false;
 		}