docs: public static <K1, K2, V> ImmutableMap<K2, V> copyWithKeysTransformedByInjection(
        final Map<K1, V> map, final Function<? super K1, K2> injection) {
      final ImmutableMap.Builder<K2, V> ret = ImmutableMap.builder();
      for (final Map.Entry<K1, V> entry : map.entrySet()) {
        ret.put(injection.apply(entry.getKey()), entry.getValue());
      }
      return ret.build();
    }