EXPRESSION vs FACTOR on NULL (no data)

Hi Experts,

I'm using BPC 10 NW. I have a question about the execution of the syntax: *REC(EXPRESSION=%VALUE%....

Here is my script:

*XDIM_MEMBERSET TIME = %TIME_SET%

*XDIM_MEMBERSET CATEGORY = Actual

*XDIM_MEMBERSET AUDITTRAIL =*

*XDIM_MEMBERSET MEASURES = YTD

*XDIM_MEMBERSET SCOPE = %SCOPE_SET%

*XDIM_MEMBERSET RPTCURRENCY = *

*XDIM_MEMBERSET ENTITY = *

*XDIM_MEMBERSET INTERCO = *

*XDIM_MEMBERSET FLOW = F99

*WHEN ACCOUNT.DIMLIST

*IS BS

*REC(EXPRESSION=%VALUE% - ([FLOW].[F00]),FLOW=F20)

*ENDWHEN

*COMMIT

Basicly, i need to calculate F20 = F99 - F00

Here is my data, after running the logic script

F20 for Account3 is not calculated, because F99 is empty and it seems that when the scoping returns no data, the record syntax wont calculates anything. Right now i used FACTOR, and the result is correct. Here's my script

*XDIM_MEMBERSET FLOW = F99, F00

*WHEN FLOW

*IS F99

*REC(FACTOR=1, FLOW=F20)

*ELSE

*REC(FACTOR=-1, FLOW=F20)

*ENDWHEN

*COMMIT

I'm curious on how the logic works and is there any other way to use the EXPRESSION syntax on the situation like this?

Thanks for helping.