static <A, B, C, D> L<T3<A, B, C>> collectThreeFieldsAsTriple(fS fieldA, fS fieldB, fS fieldC, Iterable<D> l) {
  ret map(l, func(C c) -> T3<A, B, C> {
    t3((A) getOpt(c, fieldA), (B) getOpt(c, fieldB), (C) getOpt(c, fieldC)) });
}