// hopefully covers all cases :)
static S safeSubstring(S s, int x, int y) {
  if (s == null) return null;
  if (x < 0) x = 0;
  if (x > s.length()) return "";
  if (y < x) y = x;
  if (y > s.length()) y = s.length();
  return s.substring(x, y);
}

static S safeSubstring(S s, int x) {
  ret safeSubstring(s, x, l(s));
}