SQL in RPGIV Error Message

[Justin Houchin <justinh@xxxxxxxxxxxxx>]

Hi Everyone,
   I have the following SQL Statement executing in a RPGIV program.  
Through debugging the SQL return codes, I receive the following messages 
once the statement executes:

SQLCOD = -305
SQLSTT = 22002

The SQLSTT error code 22002 means this: "A null value, or absence of an 
indicator parameter was detected; for example, the null value cannot be 
assigned to a host variable, because no indicator variable is specified".

Here is the datastructure I am reading the statement into:
    D Hardware        DS
    D  LnPart#                      
15                                        
    D  LnWh                           
2                                        
    D  LnInvType                    
1                                        
    D  LnDesc                       
30                                        
    D  LnQty                           9  
2                                    
    D  LnPackSep                   
2                                       
Note: It is possible for LnPackSep to get a null value, maybe this is 
the problem????

Here is the SQL statement:

SELECT PMP.PMPART, M3P.M3WH, ISP.ISITYP, PMP.PMDESC, WFP.WFVAL,    
SUM(M3P.ML3RQ) AS REQ_QTY                                          
FROM M3P, PMP, ISP, O6PWO                                          
LEFT JOIN WFP ON (WFP.WFSEGN = 'D.COLOR') AND                      
                (WFP.WFORD# = O6PWO.O6ORD#) AND                   
                (WFP.WFSUFX = O6PWO.O6SUFX) AND                   
                (WFP.WFITEM = O6PWO.O6ITEM)                       
WHERE (M3P.M3PN=PMP.PMPART) AND                                    
(CHAR(M3P.M3ON) = O6PWO.O6WO#) AND                                 
(M3P.M3PN = ISP.ISPART) AND                                        
((O6PWO.O6ORD# = 1023 AND O6PWO.O6SUFX=0) OR                       
(O6PWO.O6ORD# = 1025 AND O6PWO.O6SUFX = 0)) AND                    
ISP.ISWH = M3P.M3WH                                                
GROUP BY PMP.PMPART, M3P.M3WH, ISP.ISITYP, PMP.PMDESC, WFP.WFVAL   
ORDER BY M3P.M3WH, ISP.ISITYP,PMP.PMPART

The program worked fine until I added the 4 lines of SQL statement to 
left join the WFP file.  Also the above statement works correctly using 
the interactive SQL utility (STRSQL).  I have a feeling the problem has 
to do with the LnPackShp variable receiveing a null value, but I am not 
for sure and do not know how to correct the problem. Any help would much 
be appreciated.

Thanks.
Justin Houchin