Clearing a previously not empty text filter will not update livetable permalink properly

The livetable currently only updates its permalink (hash) using filters when their value is not null. This can leave previously non-empty filters in the hash, which is wrong.

To reproduce:

• Type "abc" in a text filter
• Type 3 times the backspace key
• Refresh the page

You will see the filter has been saved in the permalink as "a" while it should have been empty