Instead of populating the zero values using the missing cell property, you can try wrapping your expression in alt() (it acts like isnull() or coalesce() in SQL):
alt(sum(YourField), 0)
alt(case1[ , case2 , case3 , ...] , else)
The alt function returns the first of the parameters that has a valid number representation. If no such match is found, the last parameter will be returned. Any number of parameters can be used.
Example:
alt( date#( dat , 'YYYY/MM/DD' ),
date#( dat , 'MM/DD/YYYY' ),
date#( dat , 'MM/DD/YY' ),
'No valid date' )
Will test if the field date contains a date according to any of the three specified date formats. If so, it will return the original string and a valid number representation of a date. If no match is found, the text 'No valid date' will be returned (without any valid number representation).
