Consistently declare Object::equals argument as @Nullable

spring-test/src/main/java/org/springframework/test/context/support/DynamicPropertiesContextCustomizer.java

@@ -26,6 +26,7 @@ import java.util.function.Supplier;
 
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.core.env.MutablePropertySources;
+import org.springframework.lang.Nullable;
 import org.springframework.test.context.ContextCustomizer;
 import org.springframework.test.context.DynamicPropertyRegistry;
 import org.springframework.test.context.DynamicPropertySource;
@@ -96,7 +97,7 @@ class DynamicPropertiesContextCustomizer implements ContextCustomizer {
 	}
 
 	@Override
-	public boolean equals(Object obj) {
+	public boolean equals(@Nullable Object obj) {
 		if (this == obj) {
 			return true;
 		}

spring-test/src/main/java/org/springframework/test/web/reactive/server/XpathAssertions.java

@@ -190,7 +190,7 @@ public class XpathAssertions {
 
 
 	@Override
-	public boolean equals(Object obj) {
+	public boolean equals(@Nullable Object obj) {
 		throw new AssertionError("Object#equals is disabled " +
 				"to avoid being used in error instead of XPathAssertions#isEqualTo(String).");
 	}