Empty query as in
This has been most relevant in some applications, that I upgraded today from v0.6 to recent trunk with devastating effect on the whole environments. In short, I had to temporarily disable KeywordSuggestPlugin installed there as well, and only later found a quick but ugly hack, to get it working again (see #7856).
It looks like KeywordSuggestPlugin has been built on a default query behavior to return all known tags, that got lost in later versions of TagsPlugin. So it should be fixed here, or I totally mistake the situation.