Null Customer Count ,

Hi,

how to take null customer Count ,i have applied following formula,it is showing Count value,

=Sum(If(IsNull([Completed]);1;0)ForEach([Customer/Prospect ID Key])Where([V_Callmon      todate]Between(ToDate("04.2013";"MM.yyyy");ToDate("03.2014";"MM.yyyy"))))

Actual Count is 1517..

find the screen shot..