decode static method Null safety

Implementation

static RasterLayer decode(String properties) {
  var map = json.decode(properties);
  if (map["layout"] == null) {
    map["layout"] = {};
  }
  if (map["paint"] == null) {
    map["paint"] = {};
  }
  return RasterLayer(
    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"])),
    rasterBrightnessMax: map["paint"]["raster-brightness-max"] is num?
        ? (map["paint"]["raster-brightness-max"] as num?)?.toDouble()
        : null,
    rasterBrightnessMin: map["paint"]["raster-brightness-min"] is num?
        ? (map["paint"]["raster-brightness-min"] as num?)?.toDouble()
        : null,
    rasterContrast: map["paint"]["raster-contrast"] is num?
        ? (map["paint"]["raster-contrast"] as num?)?.toDouble()
        : null,
    rasterFadeDuration: map["paint"]["raster-fade-duration"] is num?
        ? (map["paint"]["raster-fade-duration"] as num?)?.toDouble()
        : null,
    rasterHueRotate: map["paint"]["raster-hue-rotate"] is num?
        ? (map["paint"]["raster-hue-rotate"] as num?)?.toDouble()
        : null,
    rasterOpacity: map["paint"]["raster-opacity"] is num?
        ? (map["paint"]["raster-opacity"] as num?)?.toDouble()
        : null,
    rasterResampling: map["paint"]["raster-resampling"] == null
        ? null
        : RasterResampling.values.firstWhere((e) => e
            .toString()
            .split('.')
            .last
            .toLowerCase()
            .contains(map["paint"]["raster-resampling"])),
    rasterSaturation: map["paint"]["raster-saturation"] is num?
        ? (map["paint"]["raster-saturation"] as num?)?.toDouble()
        : null,
  );
}