Inserting N/A in Report if Data is Blank CR 8.5

Hi there:

i am using Crystal Reports 8.5 and I need to insert N/A into fields that have no records.  I have tried the following formula and it doesn't work:

if not ISNULL({POTENTIAL_CLAIMANT_VIEW_MS.PATIENT_ID_NUM})

Then true

else false

I have also tried this:

stringvar formula:="";

if is notnull({POTENTIAL_CLAIMANT_VIEW_MS.PATIENT_ID_NUM})

then formula := "000000"

else 

{POTENTIAL_CLAIMANT_VIEW_MS.PATIENT_ID_NUM}

Both formulas produce results of all or none, so they are not really evaluating if the record exists or not.

Any suggestions or ideas?  Thanks so much!

Brett