avoid keyerrors on failed calcs where no tables returned
avoid keyerrors on failed calcs where no tables returned

OpenSourcePolicyCenter/webapp-public,OpenSourcePolicyCenter/webapp-public,OpenSourcePolicyCenter/PolicyBrain,OpenSourcePolicyCenter/PolicyBrain,OpenSourcePolicyCenter/PolicyBrain,OpenSourcePolicyCenter/webapp-public,OpenSourcePolicyCenter/PolicyBrain,OpenSourcePolicyCenter/webapp-public