Guard against uncountable tag values
As of PHP 7.2 counting false or null raises a "Warning: count(): Parameter must be an array or an object that implements Countable".
Bug: T182377
Bug: T196793
Change-Id: I7ca38bc55ae04f68106fe0d27c7d496da1538459
(cherry picked from commit 61af022e5f8e06c2588a8fc3fd003f52bdb85b08)