Currently there is no easy way to do that.
We have a plan to add a special "x" button on the right of the filter editor, i.e. the text-box. This "x" will assign null as the value, since there is no other easy way to enter null in a text-box. This will look like just the "Search Programs and Filter" text box when you click the Windows7 Start Button.
What do you think? Will this be the best approach? In case you have some ideas on how to implement filtering by null from the UI, could you please share them with us and we will log them.
Thanks in advance.
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