Add `@Nullable` to ResponseEntity generic type

Signed-off-by: Tran Ngoc Nhan <ngocnhan.tran1996@gmail.com>

spring-web/src/main/java/org/springframework/http/HttpEntity.java

@@ -56,7 +56,7 @@ import org.springframework.util.ObjectUtils;
  * @see #getBody()
  * @see #getHeaders()
  */
-public class HttpEntity<T> {
+public class HttpEntity<T extends @Nullable Object> {
 
 	/**
 	 * An {@code HttpEntity} instance with a {@code null} body and

spring-web/src/main/java/org/springframework/http/ResponseEntity.java

@@ -78,7 +78,7 @@ import org.springframework.util.ObjectUtils;
  * @see org.springframework.web.client.RestOperations#getForEntity(URI, Class)
  * @see RequestEntity
  */
-public class ResponseEntity<T> extends HttpEntity<T> {
+public class ResponseEntity<T extends @Nullable Object> extends HttpEntity<T> {
 
 	private final HttpStatusCode status;
 
@@ -261,7 +261,7 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 	 * @return the created {@code ResponseEntity}
 	 * @since 4.1
 	 */
-	public static <T> ResponseEntity<T> ok(@Nullable T body) {
+	public static <T extends @Nullable Object> ResponseEntity<T> ok(@Nullable T body) {
 		return ok().body(body);
 	}
 
@@ -308,7 +308,7 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 	 * @return the created {@code ResponseEntity}
 	 * @since 6.0.5
 	 */
-	public static <T> ResponseEntity<T> ofNullable(@Nullable T body) {
+	public static <T extends @Nullable Object> ResponseEntity<T> ofNullable(@Nullable T body) {
 		if (body == null) {
 			return notFound().build();
 		}
@@ -658,7 +658,7 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 		}
 
 		@Override
-		public <T> ResponseEntity<T> body(@Nullable T body) {
+		public <T extends @Nullable Object> ResponseEntity<T> body(@Nullable T body) {
 			return new ResponseEntity<>(body, this.headers, this.statusCode);
 		}
 	}

spring-web/src/test/kotlin/org/springframework/http/ResponseEntityKotlinTests.kt

@@ -43,4 +43,21 @@ class ResponseEntityKotlinTests {
 		assertThat(responseEntity.body).isNull()
 	}
 
+
+	@Test
+	fun ofNullNullableType() {
+		val responseEntity = ResponseEntity.ofNullable<Int?>(null)
+		assertThat(responseEntity).isNotNull()
+		assertThat(responseEntity.statusCode).isEqualTo(HttpStatus.NOT_FOUND)
+		assertThat(responseEntity.body).isNull()
+	}
+
+	@Test
+	fun okNullNullableType() {
+		val responseEntity = ResponseEntity.ok<String?>(null)
+		assertThat(responseEntity).isNotNull()
+		assertThat(responseEntity.statusCode).isEqualTo(HttpStatus.OK)
+		assertThat(responseEntity.body).isNull()
+	}
+
 }