Create ISERROR function

[brianvigus]

I recently had an error in a module because an expected variable was not present coming into a formula tool.  My variable, "MONDAY" was not present and the formula MONDAY/3 failed.  The workaround was to union all days into the incoming data and things worked fine.  I would have liked to have an Excel formula like this instead:

IF ISERROR([Monday]/3) THEN 0 ELSE [Monday]/3 ENDIF

Thanks