private function generateVariableIdToVariableUsageMap()
    {
        if (!empty($this->_variableUsageInstances)) {
            foreach (array_values($this->_variableUsageInstances) as $variableUsage) {
                $this->_variableIdToVariableUsageInstanceMap[$variableUsage->getId()] = $variableUsage;
            }
        }
    }