code: @NonNull
    public RequestCreator placeholder(@NonNull Drawable placeholderDrawable) {
      if (!setPlaceholder) {
        throw new IllegalStateException("Already explicitly declared as no placeholder.");
      }
      if (placeholderResId != 0) {
        throw new IllegalStateException("Placeholder image already set.");
      }
      this.placeholderDrawable = placeholderDrawable;
      return this;
    }
docs: A placeholder drawable to be used while the image is being loaded. If the requested image is
  not immediately available in the memory cache then this resource will be set on the target
  {@link ImageView}.
  <p>
  If you are not using a placeholder image but want to clear an existing image (such as when
  used in an {@link android.widget.Adapter adapter}), pass in {@code null}.