Weeknumber shows 53 for null values

[TechR21]

I created a measure for the weeknumbers based on a completiondate in my table:

Weeknr completed = WEEKNUM ( [completiondate] )

But when the value is null (meaning, the ticket is not completed yet, so open) it shows a number 53 as weeknumber.

How can I change this? i do want to have the possibility to use this value in visuals, to see how many are still not completed

[amitchandak]

@TechR21 ,

Try like

Weeknr completed = if(isblank([completiondate]) , blank(), WEEKNUM ( [completiondate] ) )