original_string: protected function _key($key)
      {
          $key = $this->key($key);
          if ($key === false) {
              throw new InvalidArgumentException('An empty value is not valid as a cache key');
          }
  
          return $this->_config['prefix'] . $key;
      }
code: protected function _key($key)
      {
          $key = $this->key($key);
          if ($key === false) {
              throw new InvalidArgumentException('An empty value is not valid as a cache key');
          }
  
          return $this->_config['prefix'] . $key;
      }
code_tokens: protected function _key ( $ key ) { $ key = $ this -> key ( $ key ) ; if ( $ key === false ) { throw new InvalidArgumentException ( 'An empty value is not valid as a cache key' ) ; } return $ this -> _config [ 'prefix' ] . $ key ; }
docstring: Generates a safe key, taking account of the configured key prefix
  
  @param string $key the key passed over
  @return mixed string $key or false
  @throws \InvalidArgumentException If key's value is empty
docstring_tokens: Generates a safe key taking account of the configured key prefix