Consistently declare Object::equals argument as @Nullable

spring-jms/src/test/java/org/springframework/jms/support/converter/MappingJackson2MessageConverterTests.java

@@ -33,6 +33,7 @@ import org.junit.jupiter.api.Test;
 import org.mockito.stubbing.Answer;
 
 import org.springframework.core.MethodParameter;
+import org.springframework.lang.Nullable;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
@@ -276,7 +277,7 @@ class MappingJackson2MessageConverterTests {
 		}
 
 		@Override
-		public boolean equals(Object o) {
+		public boolean equals(@Nullable Object o) {
 			if (this == o) {
 				return true;
 			}