Unexpected result from UDTF

Hi All, I'm testing a UDTF and don't understand why the results are
empty when I call the UDTF with no parameters.

CREATE OR REPLACE FUNCTION mylib.Display_ChkJrn (
fromDate DATE DEFAULT '2023-08-27',
toDate DATE DEFAULT CURRENT_DATE,
usr CHAR(10) DEFAULT '' )
RETURNS TABLE (
joobj CHAR(10),
....
pgmtext CHAR(50))
LANGUAGE SQL
NO EXTERNAL ACTION
DISALLOW PARALLEL
SET OPTION COMMIT=*NONE,USRPRF=*OWNER,DATFMT=*ISO
RETURN
SELECT *
FROM mylib.chkjrn
-- WHERE jodate BETWEEN fromDate AND toDate
-- AND jouser <> usr
ORDER BY jodate DESC, joseqn;

**Note the WHERE clause is commented out.

So if I call Dispay_Chkjrn with no parameters I expected all rows would be
returned. But actually no rows are returned.

SELECT * FROM TABLE(mylib.Display_ChkJrn()) x;

But what is really confusing me is if I populate one of the parameters then
all rows are returned as expected.

SELECT * FROM TABLE(mylib.Display_ChkJrn(fromDate=>'2023-11-01')) x;

Since the WHERE clause is commented out in the UDTF then I would have
expected the passing parameters or not would have no effect on the
resultset and either way all rows would be returned.

Can anyone explain this?

Thanks,

Rob