code: public static <A, B> Optional<Map<A, B>> dotGetMap(final Map map, final String pathString) {
          return dotGet(map, Map.class, pathString).map(m -> (Map<A, B>) m);
      }
docs: Get map value by path.
  @param <A> map key type
  @param <B> map value type
  @param map subject
  @param pathString nodes to walk in map
  @return value