docs: public static <K, V> Map<K, V> wrap(final Multimap<K, V> source) {
          if (source != null && !source.isEmpty()) {
              val inner = source.asMap();
              val map = new HashMap<Object, Object>();
              inner.forEach((k, v) -> map.put(k, wrap(v)));
              return (Map) map;
          }
          return new HashMap<>(0);
      }