Allow YAML processors to create a flattened map with nulls included

spring-beans/src/main/java/org/springframework/beans/factory/config/YamlProcessor.java

@@ -304,13 +304,32 @@ private boolean process(Map<String, Object> map, MatchCallback callback) {
 	 * @since 4.1.3
 	 */
 	protected final Map<String, Object> getFlattenedMap(Map<String, Object> source) {
+		return getFlattenedMap(source, false);
+	}
+
+	/**
+	 * Return a flattened version of the given map, recursively following any nested Map
+	 * or Collection values. Entries from the resulting map retain the same order as the
+	 * source. When called with the Map from a {@link MatchCallback} the result will
+	 * contain the same values as the {@link MatchCallback} Properties.
+	 * @param source the source map
+	 * @param includeNulls if {@code null} entries can be included in the result
+	 * @return a flattened map
+	 * @since 7.0.4
+	 */
+	protected final Map<String, Object> getFlattenedMap(Map<String, Object> source, boolean includeNulls) {
 		Map<String, Object> result = new LinkedHashMap<>();
-		buildFlattenedMap(result, source, null);
+		buildFlattenedMap(result, source, null, includeNulls);
 		return result;
 	}
 
 	@SuppressWarnings({"rawtypes", "unchecked"})
-	private void buildFlattenedMap(Map<String, Object> result, Map<String, Object> source, @Nullable String path) {
+	private void buildFlattenedMap(Map<String, Object> result, Map<String, Object> source, @Nullable String path,
+			boolean includeNulls) {
+		if (includeNulls && source.isEmpty()) {
+			result.put(path, null);
+			return;
+		}
 		source.forEach((key, value) -> {
 			if (StringUtils.hasText(path)) {
 				if (key.startsWith("[")) {
@@ -325,7 +344,7 @@ private void buildFlattenedMap(Map<String, Object> result, Map<String, Object> s
 			}
 			else if (value instanceof Map map) {
 				// Need a compound key
-				buildFlattenedMap(result, map, key);
+				buildFlattenedMap(result, map, key, includeNulls);
 			}
 			else if (value instanceof Collection collection) {
 				// Need a compound key
@@ -336,7 +355,7 @@ else if (value instanceof Collection collection) {
 					int count = 0;
 					for (Object object : collection) {
 						buildFlattenedMap(result, Collections.singletonMap(
-								"[" + (count++) + "]", object), key);
+								"[" + (count++) + "]", object), key, includeNulls);
 					}
 				}
 			}

spring-beans/src/test/java/org/springframework/beans/factory/config/YamlProcessorTests.java

@@ -44,8 +44,7 @@
  */
 class YamlProcessorTests {
 
-	private final YamlProcessor processor = new YamlProcessor() {
-	};
+	private final TestYamlProcessor processor = new TestYamlProcessor();
 
 
 	@Test
@@ -182,8 +181,33 @@ void customTypeNotSupportedDueToExplicitConfiguration() {
 				.withMessageContaining("Global tag is not allowed: tag:yaml.org,2002:java.net.URL");
 	}
 
+	@Test
+	void processAndFlattenWithoutIncludedNulls() {
+		setYaml("foo: bar\nbar:\n spam: {}");
+		Map<String, Object> flattened = this.processor.processAndFlatten(false);
+		assertThat(flattened).containsEntry("foo", "bar").doesNotContainKey("bar.spam").hasSize(1);
+	}
+
+	@Test
+	void processAndFlattenWithIncludedNulls() {
+		setYaml("foo: bar\nbar:\n spam: {}");
+		Map<String, Object> flattened = this.processor.processAndFlatten(true);
+		assertThat(flattened).containsEntry("foo", "bar").containsEntry("bar.spam", null).hasSize(2);
+	}
+
 	private void setYaml(String yaml) {
 		this.processor.setResources(new ByteArrayResource(yaml.getBytes()));
 	}
 
+	private static class TestYamlProcessor extends YamlProcessor {
+
+		Map<String, Object> processAndFlatten(boolean includeNulls) {
+			Map<String, Object> flattened = new LinkedHashMap<>();
+			process((properties, map) -> flattened.putAll(getFlattenedMap(map, includeNulls)));
+			return flattened;
+		}
+
+
+	}
+
 }