docs: @NonNull
    public RequestCreator error(@NonNull Drawable errorDrawable) {
      if (errorDrawable == null) {
        throw new IllegalArgumentException("Error image may not be null.");
      }
      if (errorResId != 0) {
        throw new IllegalStateException("Error image already set.");
      }
      this.errorDrawable = errorDrawable;
      return this;
    }