pretty bank code in flutter | dart

pretty_bank_code.dart

void main() {
  var item = "12345678911234567891";
  print(prettyBankCode(item)); // 1234 5678 9112 3456 7891
}

prettyBankCode(item){
  if(item != null && item.length == 20){
    var code = item.substring(0,4);
    code  = code + ' ' + item.substring(4,8);
    code  = code + ' ' + item.substring(8,12);
    code  = code + ' ' + item.substring(12,16);
    code  = code + ' ' + item.substring(16,20);
    return code;
  }
  return item;
}