Fix compose file generation for empty services

See gh-1735

Signed-off-by: varunu28 <varun.u28@gmail.com>

Author: varunu28

initializr-generator/src/main/java/io/spring/initializr/generator/container/docker/compose/ComposeFileWriter.java

@@ -40,6 +40,10 @@ public class ComposeFileWriter {
 	 * @param compose the compose file to write
 	 */
 	public void writeTo(IndentingWriter writer, ComposeFile compose) {
+		if (compose.services().isEmpty()) {
+			writer.println("services: {}");
+			return;
+		}
 		writer.println("services:");
 		compose.services()
 			.values()

initializr-generator/src/test/java/io/spring/initializr/generator/container/docker/compose/ComposeFileWriterTests.java

@@ -91,6 +91,14 @@ void servicesAreOrderedByName() {
 				""");
 	}
 
+	@Test
+	void servicesWithNoEntriesWrittenAsEmptyMap() {
+		ComposeFile file = new ComposeFile();
+		assertThat(write(file)).isEqualToIgnoringNewLines("""
+				services: {}
+				""");
+	}
+
 	private Consumer<Builder> withSuffix(int suffix) {
 		return (builder) -> builder.image("image-" + suffix).imageTag("image-tag-" + suffix);
 	}