public @Nullable String getImplementation() {
    if (testServiceImplementation != null && ApplicationManager.getApplication().isUnitTestMode()) {
      return testServiceImplementation;
    }
    else if (headlessImplementation != null && ApplicationManager.getApplication().isHeadlessEnvironment()) {
      return headlessImplementation;
    }
    else {
      return serviceImplementation;
    }
  }
public @Nullable String getImplementation()