Add a properties setter to ProblemDetail

Mainly to allow Kotlin idiomatic properties assignment.

Closes gh-31430

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

@@ -216,6 +216,18 @@ public class ProblemDetail {
 		this.properties.put(name, value);
 	}
 
+	/**
+	 * Setter for the {@link #getProperties() properties map}.
+	 * <p>By default, this is not set.
+	 * <p>When Jackson JSON is present on the classpath, any properties set here
+	 * are rendered as top level key-value pairs in the output JSON. Otherwise,
+	 * they are rendered as a {@code "properties"} sub-map.
+	 * @param properties the properties map
+	 */
+	public void setProperties(@Nullable Map<String, Object> properties) {
+		this.properties = properties;
+	}
+
 	/**
 	 * Return a generic map of properties that are not known ahead of time,
 	 * possibly {@code null} if no properties have been added. To add a property,

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

@@ -0,0 +1,34 @@
+/*
+ * 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.assertThat
+import org.junit.jupiter.api.Test
+
+/**
+ * Kotlin tests for [ProblemDetail].
+ */
+class KotlinProblemDetailTests {
+
+	@Test // gh-31430
+	fun propertiesSetter() {
+		val problemDetail = ProblemDetail()
+		val map = mapOf("foo" to "bar")
+		problemDetail.properties = map
+		assertThat(problemDetail.properties).isEqualTo(map)
+	}
+
+}