Polish "Fix potential NPE in GraylogExtendedLogFormatProperties"

See gh-43863

Author: snicoll

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/structured/GraylogExtendedLogFormatProperties.java

@@ -32,7 +32,7 @@
  */
 public record GraylogExtendedLogFormatProperties(String host, Service service) {
 
-	static final GraylogExtendedLogFormatProperties NONE = new GraylogExtendedLogFormatProperties(null, Service.NONE);
+	static final GraylogExtendedLogFormatProperties NONE = new GraylogExtendedLogFormatProperties(null, null);
 
 	public GraylogExtendedLogFormatProperties(String host, Service service) {
 		this.host = host;

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/structured/GraylogExtendedLogFormatPropertiesTests.java

@@ -46,7 +46,7 @@ void getBindsFromEnvironmentWhenHostIsPresentAndServiceIsMissing() {
 		MockEnvironment environment = new MockEnvironment();
 		environment.setProperty("logging.structured.gelf.host", "spring");
 		GraylogExtendedLogFormatProperties properties = GraylogExtendedLogFormatProperties.get(environment);
-		assertThat(properties).isEqualTo(new GraylogExtendedLogFormatProperties("spring", Service.NONE));
+		assertThat(properties).isEqualTo(new GraylogExtendedLogFormatProperties("spring", new Service(null)));
 	}
 
 	@Test
@@ -58,6 +58,15 @@ void getBindsFromEnvironmentWhenHostIsPresentAndServiceIsMissingUsesApplicationV
 		assertThat(properties).isEqualTo(new GraylogExtendedLogFormatProperties("spring", new Service("1.2.3")));
 	}
 
+	@Test
+	void getBindsFromEnvironmentWhenVersionIsPresentAndHostIsMissingUsesApplicationName() {
+		MockEnvironment environment = new MockEnvironment();
+		environment.setProperty("spring.application.name", "spring");
+		environment.setProperty("logging.structured.gelf.service.version", "1.2.3");
+		GraylogExtendedLogFormatProperties properties = GraylogExtendedLogFormatProperties.get(environment);
+		assertThat(properties).isEqualTo(new GraylogExtendedLogFormatProperties("spring", new Service("1.2.3")));
+	}
+
 	@Test
 	void getWhenNoServiceNameUsesApplicationName() {
 		MockEnvironment environment = new MockEnvironment();