private void setResult(@Nullable LottieResult<T> result) {
    if (this.result != null) {
      throw new IllegalStateException("A task may only be set once.");
    }
    this.result = result;
    notifyListeners();
  }
runNow is only used for testing.
lottie/src/main/java/com/airbnb/lottie/LottieTask.java