Question on how Date parameter in sql procedure is handled by RPG.

I apologize if this is the wrong mailing list but it does have to do with RPG in the end.

I completed the coding and began testing for an enhancement to an existing external stored procedure. I was adding a new input parameter of type DATE. During testing I was surprised that the CURRENT_DATE was being assigned in certain circumstances.

I tested it with different values and here are the results

Value passed Value in RPG program
'0001-01-01' '0001-01-01'
'2015-12-31' '2015-12-31'
' ' (quote blank quote) '2016-01-05' (current_date)
'' (quote quote) '2016-01-05' (current_date)
0 (zero) '2016-01-05' (current_date)
'2016-02-30' SQL State: 07006, Vendor Code: -99999, Message: Data type mismatch. (2016-02-30) (The RPG is never called)

I can understand the first two rows and the value in the RPG program is expected. But the values of the 3rd to 5th rows are not understood. I would think that I would get a Data Type Mismatch as is seem in the 6th row.

Can anyone explain this behavior.

Thanks and a belated Happy New Year to everyone.

Rob