static <A, B> MultiMap<A, B> multiMapFromKeyAndValueField(Collection l, S keyField, S valueField) {
  new MultiMap<A, B> mm;
  if (l != null) for (O o : l)
    mm.put((A) getOpt(o, keyField), (B) getOpt(o, valueField));
  ret mm;
}

static <A, B> MultiMap<A, B> multiMapFromKeyAndValueField(S keyField, S valueField, Collection l) {
  ret multiMapFromKeyAndValueField(l, keyField, valueField);
}