Helm In Combat is an addon that automatically shows your helm whenever you enter combat, and hides your helm whenever you exit combat.
With the release of the Legion Pre-expansion Patch 7.0, this addon has broken for the first time in almost 7 years. Blizzard has removed the ShowHelm Lua function used to toggle the display of the helm in favor of using the new wardrobe system at a transmogrification NPC. As it stands right now, I believe this addon is impossible to fix. If I come up with any workaround, I will post an update.