static <A> A assertNotNullVerbose(A y) {
  assertNotNullVerbose((S) null, y);
  ret y;
}

static <A> A assertNotNullVerbose(S msg, A y) {
  if (y == null) {
    fail((msg != null ? msg + ": " : "") + "value is null");
  } else
    print("OK (not null): " + y);
  ret y;
}

Began life as a copy of #1002936