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