static O[] paramsPlus_noOverwrite(O[] a1, O... a2) {  
  if (a2 == null) ret a1;
  if (a1 == null) ret a2;
  if (l(a1) == 1 && a1[0] instanceof Map)
    ret new O[] { mapPlus((Map) a1[0], a2) };
  assertEvenLength(a1);
  assertEvenLength(a2);
  Map map = paramsToOrderedMap(a1);
  int n = l(a2);
  for (int i = 0; i < n; i += 2)
    mapPut_noOverwrite(map, a2[i], a2[i+1]);
  ret mapToParams(map);
}

Began life as a copy of #1022114