code: function lpop(key, req) {
    var val = this.getKey(key, req);
    if(val === undefined) return null;
    var element = val.lpop();
    if(val.llen() === 0) {
      this.delKey(key, req);
    }
    return element;
  }
docs: Removes and returns the first element of the list stored at key.