Update MapEntry::hashCode to honor Map.Entry::hashCode contract (assertj#2503)

Co-authored-by: Stefano Cordio <stefano_cordio@epam.com>

Author: bjhargrave

src/main/java/org/assertj/core/data/MapEntry.java

@@ -58,7 +58,7 @@ public boolean equals(Object object) {
 
   @Override
   public int hashCode() {
-    return Objects.hash(key, value);
+    return Objects.hashCode(key) ^ Objects.hashCode(value);
   }
 
   @Override

src/test/java/org/assertj/core/data/MapEntry_Test.java

@@ -16,13 +16,15 @@
 import static org.assertj.core.api.BDDAssertions.then;
 import static org.assertj.core.data.MapEntry.entry;
 
+import java.util.Objects;
+
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 import nl.jqno.equalsverifier.EqualsVerifier;
 
 /**
- * Tests for {@link MapEntry}.
- *
  * @author Alex Ruiz
  */
 class MapEntry_Test {
@@ -34,6 +36,23 @@ void should_honor_equals_contract() {
                   .verify();
   }
 
+  @ParameterizedTest
+  @CsvSource({
+    "name, Yoda",
+    " , Yoda",
+    "name, ",
+    " , ",
+  })
+  void should_honor_Entry_hashCode_contract(String key, String value) {
+    // GIVEN
+    MapEntry<String, String> underTest = entry(key, value);
+    int expected = Objects.hashCode(key) ^ Objects.hashCode(value);
+    // WHEN
+    int result = underTest.hashCode();
+    // THEN
+    then(result).isEqualTo(expected);
+  }
+
   @Test
   void setValue_should_fail() {
     // GIVEN