当"switch-case“中有返回语句时，如何在Dart中避免”不返回“警告？

String getDayOfWeek(int day) {
  String dayName;

  switch (day) {
    case 1:
      dayName = "Monday";
      break;
    case 2:
      dayName = "Tuesday";
      break;
    case 3:
      dayName = "Wednesday";
      break;
    case 4:
      dayName = "Thursday";
      break;
    case 5:
      dayName = "Friday";
      break;
    case 6:
      dayName = "Saturday";
      break;
    case 7:
      dayName = "Sunday";
      break;
    default:
      dayName = "Invalid day";
      break;
  }

  return dayName;
}