/**
* returns the string rapresentation of the
* operation property
*
* @return null|string
* @access public
*/
public function toString()
{
return !is_null($this->_operation) ? $this->_operation->toString() : null;
}
/**
* returns the string rapresentation of the
* operation property
*
* @return null|string
* @access public
*/
public function toString()
{
return !is_null($this->_operation) ? $this->_operation->toString() : null;
}