You can already use Advanced Search to find assets that have no data in specific metadata fields. For example, with text attributes (like 'Description') you can just type in 'isempty' and hit 'Search' to find all assets with no value in this field.
This is also supported for checklists and dropdowns, where you'll see an 'Empty' option that you can select.
We've now extended this feature so that it can be used via the Filter Bar. You can type 'isempty' into text fields or use the new 'Empty' option that appears in dropdowns or checklists.