private function _validateNaturalWayArgument($way)
	{
		if(!$way)
		{
			return null;
		}
		if($way !== 'inner' && $way !== 'left' && $way !== 'leftOuter' && $way !== 'right' && $way !== 'rightOuter')
		{
			throw new \UnexpectedValueException('the way argument has to be type of inner, left[Outer], right[Outer]');
		}

		return $way;
	}