BRF Plus Formula Context

Hi all,

I use BRF Plus during the Dunning Run.

I need to create a formula in BRF Plus that calculates the difference between two different dates.

I already have one formula like this, that works good:

DT_DURATION_DIFF_DAYS ( I_FKKMAGRP-AUSDT , I_FKKMAKO-LAUFD )

I used the same way in order to build the second one, that unfortunately does not work:

DT_DURATION_DIFF_DAYS ( ZZORIG_CONTEND , ZZCONT_START )

all the dates have the same format: YYYYMMDD

all the dates are passed populated (means not blank) to the BRF Plus: I checked it both from dunning run side, debugging it,  and from BRF Plus side, putting each parameter in the decision table that I use, with "is not initial" as operand: the result is the one expected, so the dates are correctly read by the BRF Plus.

But when i try to use the second formula built, unfortunately, the result is always zero (I checked it setting properly the decision table).

The only difference I can see between the first formula, that works, and the second one, that does not work, is the Context of the formula itself: in the one that works, it is correctly populated, and it is basically the same context of the function:

in the one that does not work it is blank:

since both results are in the Function context, I cannot understand why the second one is blank.

Thanks a lot for any idea.

Ermanno