code: public static Actor app(String appId) {
  		Assert.notNull(appId, "appId must not be null");
  		return new Actor(APP, appId);
  	}
docs: Create an application identifier. An application is identified by a GUID generated
  by Cloud Foundry when the application is created.
  
  @param appId the Cloud Foundry application GUID
  @return the created {@literal Actor}