Sum to have a value as zero in case not found

Hi All, I have some search criteria followed by stats as: Search ns=app1 Error | stats sum(eval(AcctNo="'1000394'")) as "FailedOccurences". In case if that AcctNo is not found in the Search, it does not display FailedOccurences. Kindly let me how can I get a value of Zero for FailedOccurences if AcctNo is not found in Search result. Thank you.