static <A, B> StringTrie<B> lambdaMapLike mapStringTrieValues(IF1<A, B> f, StringTrie<A> trie) {
  if (trie == null) null;
  new StringTrie<B> trie2;
  if (trie.value != null)
    trie2.value = f.get(trie.value);
  trie2.children = (TreeMap) mapValues(trie.children, child
    -> mapStringTrieValues(f, child));
  ret trie2;
}

Began life as a copy of #1030178