Can one keep chocolate uncovered in the freezer?
Food-safety-wise, putting chocolate in the freezer is not an issue and not even necessary.

However, quality may suffer:


Freezers do tend to have some off flavors over the time, and these can be absorbed by the food inside, if not packaged properly. To be safe, I recommend you put the chocolate bar in some kind of airtight package, either a freezer bag or a Tupperware-style box.
Humidity can be a problem for “crisp” fillings like wafers or, to a lesser extent, crispy caramel. The packaging and the chocolate coating protects the original bar, once you have eaten half, it is exposed. Unless you live in an exceptionally humid environment or store too long or in a humid environment where condensation can happen - like a freezer - , this should be a minor issue. Again, wrapping the half-eaten bar with a (mostly) airtight seal should do the trick.