static <A> Pair<S, StringTrie<A>> stringTrie_firstNodeStartingWith(StringTrie<A> trie, S string) {
  new StringBuilder buf;
  S s = string;
  while licensed {
    if (trie == null) break;
    if (empty(string)) break;
    S prefix = trie.longestLocalPrefix(s);
    if (empty(prefix)) break;
    Map.Entry<S, StringTrie<A>> e = trie.children.ceilingEntry(prefix);
    buf.append(e.getKey());
    trie = e.getValue();
    s = dropFirst(s, l(e.getKey()));
  }
  ret trie == null ? null : pair(str(buf), trie);
}

Began life as a copy of #1030183