static <A> A listGetOrCreate(L<A> l, int i, Class<? extends A> c) {
  ret listGetOrCreate(l, i, -> nuInstance(c));
}

static <A> A listGetOrCreate(L<A> l, int i, IF0<A> f) {
  if (l == null) null;
  A a = get(l, i);
  if (a == null)
    listSet(l, i, a = f!);
  ret a;
}

static <A> A nuLike listGetOrCreate(Class<? extends A> c, L<A> l, int i) {
  ret listGetOrCreate(l, i, c);
}

Began life as a copy of #1021808