getCategoryName method Null safety

Implementation

String getCategoryName(int index) {
  switch(index){
    case 0:
      return "GeneralKnowledge";
    case 1:
      return "Art";
    case 2:
      return "Entertainment";
    case 3:
      return "Science";
    case 4:
      return "Mythology";
    case 5:
      return "History";
    case 6:
      return "Sports";
    default:
      return "none";
  }
}