Get outlook Mail Messages activity - Use filter to check the empty or Null category

Hi!

My requirement is to get email from outlook folder with unassigned outlook category.
I am trying to check if category is NULL\empty then only pick email for processing.
I tried using something like following in ‘filter’ but its not working:
“[Categories]=’’”

Hi there…I hacked around for 5 hours and found no answer to this same problem…but eventually solved it myself:
this simple filter works perfectly…
“Not [categories] > 0” in the filter expression…

…it was working…until I migrated the xaml to the Enterprise environment where it no longer works??