toXML method Null safety

@override String toXML()

Convert the Svg structure to XML string

Implementation

@override
String toXML() {
  var gXml = '';
  for (var c in children) {
    gXml += '\t' + c.toXML() + '\n';
  }

  var xml =
      '<g ${attributes(id, fill, stroke, strokeWidth, strokeDasharray, style, transform, unit, visibility)} >'
      '$gXml'
      '</g>';

  return xml;
}