protected function _setStateAware($stateAware)
    {
        if ($stateAware !== null && !($stateAware instanceof StateAwareInterface)) {
            throw $this->_createInvalidArgumentException(
                $this->__('Argument is not a state aware object'),
                null,
                null,
                $stateAware
            );
        }

        $this->stateAware = $stateAware;
    }