Get Defference of null value in Pivot Table

[JonathanG]

Hi Guys,

I have a data:

Date (DD/MM/YYYY)	Place	Region	Value
01/08/2020	1	A	2
01/08/2020	1	B	7
01/08/2020	2	C	4
01/08/2020	2	D	8
01/09/2020	1	A	1
01/09/2020	1	A	9
01/09/2020	1	B	5
01/09/2020	2	C	7
01/09/2020	2	C	3

and i transform into pivot

		01/08/2020	01/09/2020
1	A	2	10
	B	7	5
2	C	4	10
	D	8	-

I use if(isnull(sum(value)),0,sum(value))-if(isnull(before(sum(value))),0,before(sum(value))) and it gives me value ONLY row A (-8), B (2), C (-6) while D returns to - instead of -8

how to get the difference if there is a null value?

Thank you