code: @Override
      public Map<String, Object> toMap() {
          Map<String, Object> map = C.newMap();
          for (Map.Entry<String, ValueObject> entry : entrySet()) {
              map.put(entry.getKey(), entry.getValue().value());
          }
          return map;
      }
docs: Returns a `Map` contains (key, value) pairs that stored in this
  `KVStore`. The value in the pair should be the {@link ValueObject#value()}
  stored in the {@link ValueObject} in this `KVStore`
  
  @return the map of key and raw value stored in this store