toOptionsJSON method 
    
    
    
  Implementation
  @override
void toOptionsJSON(StringBuffer buffer) {
  super.toOptionsJSON(buffer);
  if (callback != null) {
    buffer.writeAll(['"callback":', callback?.toJSON(), ','], '');
  }
  if (maxHeight != null) {
    buffer.writeAll(['"maxHeight":', maxHeight, ','], '');
  }
  if (maxWidth != null) {
    buffer.writeAll(['"maxWidth":', maxWidth, ','], '');
  }
  if (minHeight != null) {
    buffer.writeAll(['"minHeight":', minHeight, ','], '');
  }
  if (minWidth != null) {
    buffer.writeAll(['"minWidth":', minWidth, ','], '');
  }
}