Add ResponseEntity.ofNullable()

To deal with non-Optional nullable objects.

Closes gh-29117

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

@@ -0,0 +1,46 @@
+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.http
+
+import org.assertj.core.api.Assertions
+import org.junit.jupiter.api.Test
+
+/**
+ * Kotlin tests for [ResponseEntity].
+ *
+ * @author Sebastien Deleuze
+ */
+class KotlinResponseEntityTests {
+
+	@Test
+	fun ofNullable() {
+		val entity = 42
+		val responseEntity = ResponseEntity.ofNullable(entity)
+		Assertions.assertThat(responseEntity).isNotNull()
+		Assertions.assertThat(responseEntity.statusCode).isEqualTo(HttpStatus.OK)
+		Assertions.assertThat(responseEntity.body as Int).isEqualTo(entity)
+	}
+
+	@Test
+	fun ofNullNullable() {
+		val responseEntity = ResponseEntity.ofNullable<Int>(null)
+		Assertions.assertThat(responseEntity).isNotNull()
+		Assertions.assertThat(responseEntity.statusCode).isEqualTo(HttpStatus.NOT_FOUND)
+		Assertions.assertThat(responseEntity.body).isNull()
+	}
+
+}