code: protected function quoteIdentifier($value) {
      if ( is_null($value) )
        return 'NULL';
  
      $connection = $this->node->getConnection();
  
      $pdo = $connection->getPdo();
  
      return $pdo->quote($value);
    }
docs: Quotes an identifier for being used in a database query.
  
  @param mixed $value
  @return string