IsNotNull - in query design

Experts,

I am trying to modify the below query.  Access gives me an error of undefined function on the "IsNotNull".  I dont think I can use IsNotNull in the query.  Is there a work around or a better idea?  Please see bold    I also tried [ContractAward]<>"" but got a data type mismatch error.  Also note that the query worked fine until I added the IsNotNUll part so there is not a naming issue and if I take out the IsNotNull section then it works fine.

thank you.

MyGroup: IIf([tblStatus.Status] Like "*Awarded*" Or [tblStatus.Status] Like "Won*" Or IsNotNull([ContractAward],"Awarded",GetGroup([Projects.BidCloseDate],[Projects.ATTApprvDate],[Projects.ATCApprvDate],[Projects.ATSApprvDate],[Projects.ContractAward],[Projects.AnticipatePOSignDate],[Projects.CorpATTDate],[Projects.ExpectedContractAward])))