Add ResponseEntity.ofNullable()

To deal with non-Optional nullable objects.

Closes gh-29117

spring-web/src/test/java/org/springframework/http/ResponseEntityTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * @author Arjen Poutsma
  * @author Marcel Overdijk
  * @author Kazuki Shimizu
+ * @author Sebastien Deleuze
  */
 class ResponseEntityTests {
 
@@ -90,6 +91,25 @@ class ResponseEntityTests {
 		assertThat(responseEntity.getBody()).isNull();
 	}
 
+	@Test
+	void ofNullable() {
+		Integer entity = 42;
+		ResponseEntity<Integer> responseEntity = ResponseEntity.ofNullable(entity);
+
+		assertThat(responseEntity).isNotNull();
+		assertThat(responseEntity.getStatusCode()).isEqualTo(HttpStatus.OK);
+		assertThat((int) responseEntity.getBody()).isEqualTo((int) entity);
+	}
+
+	@Test
+	void ofNullNullable() {
+		ResponseEntity<Integer> responseEntity = ResponseEntity.ofNullable(null);
+
+		assertThat(responseEntity).isNotNull();
+		assertThat(responseEntity.getStatusCode()).isEqualTo(HttpStatus.NOT_FOUND);
+		assertThat(responseEntity.getBody()).isNull();
+	}
+
 	@Test
 	void createdLocation() {
 		URI location = URI.create("location");