private static <T> List<Keyframe<T>> parse(JsonReader reader,
      LottieComposition composition, ValueParser<T> valueParser) throws IOException {
    return KeyframesParser.parse(reader, composition, 1, valueParser, false);
  }
Will return null if the animation can't be played such as if it has expressions.
lottie/src/main/java/com/airbnb/lottie/parser/AnimatableValueParser.java