fourthStringAtIndex method Null safety

String? fourthStringAtIndex(
  1. int index
)

Implementation

String? fourthStringAtIndex(int index) {
  int max = _maxHourOfCurrentDay();
  int min = _minHourOfCurrentDay();

  if (index >= 0 && index < max - min + 1) {
    return padZero(min + index);
  }
  return null;
}