static O[] dropLastFromObjectArray(O[] a) {
  ret dropLastFromObjectArray(a, 1);
}

static O[] dropLastFromObjectArray(O[] a, int n) {
  if (a == null) null;
  n = Math.min(n, a.length);
  O[] b = new O[a.length-n];
  System.arraycopy(a, 0, b, 0, b.length);
  ret b;
}