toOptionsJSON method
Implementation
@override
void toOptionsJSON(StringBuffer buffer) {
  super.toOptionsJSON(buffer);
  if (animation != null) {
    buffer.writeAll(['"animation":', animation?.toJSON(), ','], '');
  }
  if (enabled != null) {
    buffer.writeAll(['"enabled":', enabled, ','], '');
  }
  if (opacity != null) {
    buffer.writeAll(['"opacity":', opacity, ','], '');
  }
}