LlDefineVariableExt("DATE", "(NULL)", LL_DATE_MS, NULL)
This will prevent the value from appearing in the print out. You may also configure an arbitrary hint text in the designer by using the IsNULL() function:
Cond(IsNULL(DATE), "no date")
With versions older than List & Label 11 use
LlDefineVariableExt("DATE", "1e100", LL_DATE_MS, NULL)
The value “1e100” will be intepreted as emtpy date and the output will be suppressed. Remember to use Date$(DATE) in the Designer for any date output.