decode static method Null safety

Implementation

static LineLayer decode(String properties) {
  var map = json.decode(properties);
  if (map["layout"] == null) {
    map["layout"] = {};
  }
  if (map["paint"] == null) {
    map["paint"] = {};
  }
  return LineLayer(
    id: map["id"],
    sourceId: map["source"],
    sourceLayer: map["source-layer"],
    minZoom: map["minzoom"]?.toDouble(),
    maxZoom: map["maxzoom"]?.toDouble(),
    visibility: map["layout"]["visibility"] == null
        ? Visibility.VISIBLE
        : Visibility.values.firstWhere((e) => e
            .toString()
            .split('.')
            .last
            .toLowerCase()
            .contains(map["layout"]["visibility"])),
    lineCap: map["layout"]["line-cap"] == null
        ? null
        : LineCap.values.firstWhere((e) => e
            .toString()
            .split('.')
            .last
            .toLowerCase()
            .contains(map["layout"]["line-cap"])),
    lineJoin: map["layout"]["line-join"] == null
        ? null
        : LineJoin.values.firstWhere((e) => e
            .toString()
            .split('.')
            .last
            .toLowerCase()
            .contains(map["layout"]["line-join"])),
    lineMiterLimit: map["layout"]["line-miter-limit"]?.toDouble(),
    lineRoundLimit: map["layout"]["line-round-limit"]?.toDouble(),
    lineSortKey: map["layout"]["line-sort-key"]?.toDouble(),
    lineBlur: map["paint"]["line-blur"]?.toDouble(),
    lineColor: (map["paint"]["line-color"] as List?)?.toRGBAInt(),
    lineDasharray: (map["paint"]["line-dasharray"] as List?)
        ?.map<double?>((e) => e.toDouble())
        .toList(),
    lineGapWidth: map["paint"]["line-gap-width"]?.toDouble(),
    lineGradient: (map["paint"]["line-gradient"] as List?)?.toRGBAInt(),
    lineOffset: map["paint"]["line-offset"]?.toDouble(),
    lineOpacity: map["paint"]["line-opacity"]?.toDouble(),
    linePattern: map["paint"]["line-pattern"],
    lineTranslate: (map["paint"]["line-translate"] as List?)
        ?.map<double?>((e) => e.toDouble())
        .toList(),
    lineTranslateAnchor: map["paint"]["line-translate-anchor"] == null
        ? null
        : LineTranslateAnchor.values.firstWhere((e) => e
            .toString()
            .split('.')
            .last
            .toLowerCase()
            .contains(map["paint"]["line-translate-anchor"])),
    lineTrimOffset: (map["paint"]["line-trim-offset"] as List?)
        ?.map<double?>((e) => e.toDouble())
        .toList(),
    lineWidth: map["paint"]["line-width"]?.toDouble(),
  );
}