protected function _setColumnNumber($columnNumber)
    {
        if ($columnNumber !== null) {
            try {
                $columnNumber = $this->_normalizeInt($columnNumber);
            } catch (RootException $e) {
                throw $this->_createInvalidArgumentException($this->__('Invalid column number'), null, $e, $columnNumber);
            }

            if ($columnNumber < 1) {
                throw $this->_createInvalidArgumentException($this->__('Column number must be positive'), null, null, $columnNumber);
            }
        }

        $this->columnNumber = $columnNumber;
    }