decodeMap method Null safety

Implementation

Map<String, dynamic> decodeMap(dynamic src) {
  var p = src is GsonParsable
      ? src
      : src is String
          ? GsonParsable(src)
          : throw ('The src is not a valid input to decode an Array from');
  var map = <String, dynamic>{};
  var foundComma = true;
  if (p.next() != '{') {
    throw ('Array has to start with a [');
  }
  while (p.actual() != '}') {
    if (!foundComma) {
      throw p.error('Expected "}" or ","');
    }
    foundComma = false;
    _skipIgnored(p);
    var key = '';
    if (p.actual() == '"' || p.actual() == "'") {
      key = decodeString(src);
    } else {
      while (_KEY_CHARACTERS.hasMatch(p.actual())) {
        key += p.next();
      }
    }

    _skipIgnored(p);

    if (p.actual() != ':') {
      throw p.error('Expected ":"');
    }
    p.skip();

    _skipIgnored(p);

    if (RegExp(r'''[\\[\\{\\\"\\\'0-9]''').hasMatch(p.actual()) ||
        _PURE_STRING.hasMatch(p.actual())) {
      map[key] = decode(p);
    } else {
      throw p.error('Expected "[", "\\"","\\\'", "{" or a number');
    }

    _skipIgnored(p);

    if (p.actual() == ',') {
      foundComma = true;
      p.skip();
    }
    _skipIgnored(p);
  }
  if (!p.ended) p.skip();
  return map;
}