When using category not in it excludes projects with no category value.

Summary

When using category not in (value1,value2) JQL does not return results where projects don't have a value for a category.

Steps to Reproduce

1. Create a few test projects.
2. Create a project two categories i.e. test1 & test2.
3. Add project a to category test1.
4. Run a JQL query category not in (test2).

Expected Results

JQL query should return all results where category doesn't = test 2.

Actual Results

It only includes projects that are test1 and it excludes all projects that do not have a category specified.

Workaround

In order for it to work correctly you have to include category not in (test2) OR category is empty.