code: public void setImageAssetDelegate(
        @SuppressWarnings("NullableProblems") ImageAssetDelegate assetDelegate) {
      this.imageAssetDelegate = assetDelegate;
      if (imageAssetManager != null) {
        imageAssetManager.setDelegate(assetDelegate);
      }
    }
docs: Use this if you can't bundle images with your app. This may be useful if you download the
  animations from the network or have the images saved to an SD Card. In that case, Lottie
  will defer the loading of the bitmap to this delegate.
  <p>
  Be wary if you are using many images, however. Lottie is designed to work with vector shapes
  from After Effects. If your images look like they could be represented with vector shapes,
  see if it is possible to convert them to shape layers and re-export your animation. Check
  the documentation at http://airbnb.io/lottie for more information about importing shapes from
  Sketch or Illustrator to avoid this.