notInCharClass function Null safety

int? notInCharClass(
  1. CharClass charClass,
  2. String string

Tests whether all characters of string are in the charClass. Returns null if all characters are in the charClass, otherwise the first index of string with a character not in charClass


int? notInCharClass(CharClass charClass, String string) {
  int? rc;
  final members = BaseRandom.getCharClassMembers(charClass) ?? '';
  for (var ix = 0; ix < string.length; ix++) {
    if (!members.contains(string[ix])) {
      rc = ix;
  return rc;