Filling missing values with previous data (File attached)

[#1]

Hello,

This is what I want to do:

I want to show the total stock in the past months. The stock is calculated using the current stock level with transaction history.

Problem is, when a month has no transactions, the stock level is 0. When calculating the total stock in that month, the total will be inaccurate.

Can someone please look at my Qlikview file? I have been struggling with this for the past 2 days.

Thanks in advance.

[#2]

I have like this:

=if(sum(aggr( FirstSortedValue( PartStockEnd, -Date) , Month, KeyPart))='0',Above(sum(aggr( FirstSortedValue( PartStockEnd, -Date) , Month, KeyPart))),sum(aggr( FirstSortedValue( PartStockEnd, -Date) , Month, KeyPart)))

But it shows just the same values.

and i think i know what the problem is: the transaction doesnt have records. so its not even 0, there is no record.