How can you use a Power Filter to filter for IS NULL or NOT NULL conditions?
You are trying to use a power filter with a condition that tests for a NULL value, but it does not seem to work correctly.
The Power Filter is currently designed to search for values only. If you leave the field empty (NULL value) that field is not included in the filtering. There is no current functionality that allows the configuration of the power filter to search for NULL or NOT NULL values.