toXML method Null safety

@override String toXML()

Convert the Svg structure to XML string

Implementation

@override
String toXML() {
  var pointsXML = '';
  points.forEach((p) => pointsXML += p.toXML() + ' ');

  var xml = '<polygon points="$pointsXML" '
      '${attributes(id, fill, stroke, strokeWidth, strokeDasharray, style, transform, unit, visibility)} />';
  return xml;
}