Is your feature request related to a problem? Please describe.
Currently, there is isEmpty condition, which is passed when
either "key": [] or key does not exist.

But it is not triggered if "key": null.

Describe the solution you'd like
A new condition, that can check for null.

Describe alternatives you've considered
Allow isEmpty to match with "key": null.

Additional context

Would require:

• Unit tests to check that the new condition works
• OpenAPI integration tests to make sure schema is updated properly