We have isnull and isempty operators for string fields. But it is too much "technical" for standard users. It is hard to explain difference between null and empty. It is the same for most of user. It is just "no value". There is no difference in grid view. Youll see empty space. Empty string or null value, it desn't matter. 

There should be operator to filter nulls and empty strings with one filter item. Something like "With value" and "Without value". It implements merged operators "isnull or isempty".