DAX running Total measure that does not repeat for empty rows

Hello ,

I have a straightforward running total by category ;

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But I got around this by using another measure

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Which I don't actually have in the table, but if I put in in an 'IF ' statement,

so;

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This solves the problem but is there a way I can do this without this extra measure, I've tried using a Filter expression typed into the iff statement but not got it working.
, I've attached a simple workbook show what I and I've got so far which show the problem better,