code: @Override
      public NutMap pickAndRemove(String... keys) {
          if (keys.length == 0)
              return new NutMap();
          NutMap re = new NutMap();
          for (String key : keys) {
              Object val = this.remove(key);
              re.put(key, val);
          }
          return re;
      }
docs: 从 Map 里挑选一些键生成一个新的 Map，自己同时删除这些键
  
  @param keys
  键
  @return 新 Map