public Float getOffset(LottieFrameInfo<Float> frameInfo) {
    if (value == null) {
      throw new IllegalArgumentException("You must provide a static value in the constructor " +
          ", call setValue, or override getValue.");
    }
    return value;
  }
{@link LottieValueCallback} that provides a value offset from the original animation
rather than an absolute value.
lottie/src/main/java/com/airbnb/lottie/value/LottieRelativeFloatValueCallback.java