If you right click on your "SUM([Number of Customers])" measure and select "Filter", you should see a menu similar to this one:
In the top right corner you can see there is an option for "Special" filters. Use this option to see the following menu, where you can filter to only show Non-NULL values:
Hopefully this solves your issue. Let me know if it doesn't.
Hey Chris! Thanks for your input. However, when I filter the view to show only null values, I end up with an empty view. Somehow it seems like all the null values are interpreted as non-null which is kind of strange…
I see. If the NULL values are being converted to zero, does this mean you are using the ZN() function anywhere in your calculation?
Out of curiousity, what is stopping you filtering to only see values which are >= 1 ?