code: public function offsetExists($offset)
      {
          if (!isset($this->data[$offset])) {
              $this->requestAllPages();
          }
          return isset($this->data[$offset]);
      }
docs: Whether an offset exists
  
  @param int|string $offset
  
  @return bool
  
  @see http://php.net/manual/en/arrayaccess.offsetexists.php
  ArrayAccess::offsetExists