User Defined Function Definition with Omissible Parameters

Hi All, 
        I have a user defined function as:      
CREATE FUNCTION GBCMODS/CVTTOJDEDATE (           
 DATEIN DATE )                                   
 RETURNS NUMERIC(6, 0) CAST FROM NUMERIC(6, 0)   
 LANGUAGE RPGLE                                  
 SPECIFIC GBCMODS/CVTTOJDEDATE                   
 NOT DETERMINISTIC                               
 NO SQL                                          
 RETURNS NULL ON NULL INPUT                      
 DISALLOW PARALLEL                               
 EXTERNAL NAME 'GBCMODS/PRDATES(CVTTOJDEDATE)'   
 PARAMETER STYLE DB2SQL ;     

The Program Interface to the CVTTOJDEDATE procedure has changed to:
D CvtToJDEDate    PI             6S 0                              
D  InputDate                      D   CONST OPTIONS(*OMIT)         
D  Date2DigitYY                  8    CONST OPTIONS(*NOPASS:*OMIT) 
D  Fmt2DigitYY                   7    CONST OPTIONS(*NOPASS:*OMIT)


The function no longer works within SQL. Debug shows that the function
is passing junk to the 2nd and 3rd procedure parms.
Does anyone know how to define omissible parameters on the Create
Function?  

Thanks in advance...
Steve...