decodeNumber method Null safety

Implementation

NumberValue decodeNumber(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');
  if (!RegExp(r'[0-9\.]').hasMatch(p.actual())) {
    throw p.error('Any number has to start with a number between 0 and 9');
  }
  var number = '';
  while (RegExp(r'[0-9\.]').hasMatch(p.actual())) {
    number += p.next();
  }

  NumberValue ret;

  switch (p.actual()) {
    case 'b':
      ret = Byte(int.parse(number));
      if (!p.ended) {
        p.skip();
      }
      break;
    case 's':
      ret = Short(int.parse(number));
      if (!p.ended) {
        p.skip();
      }
      break;
    case 'l':
      ret = Long(int.parse(number));
      if (!p.ended) {
        p.skip();
      }
      break;
    case 'f':
      ret = Float(double.parse(number));
      if (!p.ended) {
        p.skip();
      }
      break;
    case 'd':
      ret = Double(double.parse(number));
      if (!p.ended) {
        p.skip();
      }
      break;
    default:
      if (number.contains('.')) {
        ret = Double(double.parse(number));
      } else {
        ret = Integer(int.parse(number));
      }
      break;
  }

  return ret;
}