code: protected function _setDataKey($key)
      {
          if (!is_null($key) && !is_string($key) && !($key instanceof Stringable)) {
              throw $this->_createInvalidArgumentException($this->__('Data key must be a string or stringable'), 0, null, $key);
          }
  
          $this->dataKey = $key;
  
          return $this;
      }
docs: Assigns a data key to this instance.
  
  @since [*next-version*]
  
  @param string|Stringable|null $key The key.
  
  @throws InvalidArgumentException If the key is invalid.