Comment 4 for bug 834571

In the applications lens, line 100 of utils.vala in the applications lens considers that the old_search (null) is the same as the new_search (""). The same code is duplicated in the files lens.

But the bug also occurs with the music lens and the gwibber lens.
The probable extra cause is that a Scope has a default LensSearch active_search attribute whose search_string is "" by default
hence when getting to line 229 of unity-scope-private.vala the new "" search is discarded.