static int intSum(Collection c, S field) {
  int sum = 0;
  for (O o : unnull(c))
    sum += toInt(getOpt(o, field));
  ret sum;
}

static int intSum(Iterable<Int> l) {
  int sum = 0;
  for (Int i : unnull(l))
    if (i != null) sum += i;
  ret sum;
}

static int intSum(int... l) {
  int sum = 0;
  for (int i : unnull(l))
    sum += i;
  ret sum;
}