Showing value as a zero or a null in a bound field

I have a table in a livecycle form that is bound to fields in a SQL database.  There are both zero and null values in the database that I want to show as such in the table, but any zero values appear as blank when previewed in PDF or published.  The cell pattern is currently set to null{}|zero{}|num{z,zzz,zzz,zz9}, but changing the pattern to null{}|zero{0}|num{z,zzz,zzz,zz9} or null{}|zero{'0'}|num{z,zzz,zzz,zz9} results in this err msg:

Thanks for any help!