toOptionsJSON method
Implementation
@override
void toOptionsJSON(StringBuffer buffer) {
  super.toOptionsJSON(buffer);
  if (lineColor != null) {
    buffer.writeAll(['"lineColor":', jsonEncode(lineColor), ','], '');
  }
  if (lineWidth != null) {
    buffer.writeAll(['"lineWidth":', lineWidth, ','], '');
  }
}