protected function _getFieldMap($sourceSurveyId, $language = null)
    {
        $language = $this->_getLanguage($sourceSurveyId, $language);
        // \MUtil_Echo::track($language, $sourceSurveyId);

        if (! isset($this->_fieldMaps[$sourceSurveyId][$language])) {
            $className = $this->fieldMapClass;
            $this->_fieldMaps[$sourceSurveyId][$language] = new $className(
                    $sourceSurveyId,
                    $language,
                    $this->getSourceDatabase(),
                    $this->translate,
                    $this->addDatabasePrefix(''),
                    $this->cache,
                    $this->getId()
            );
        }

        return $this->_fieldMaps[$sourceSurveyId][$language];
    }