Avoid nil unit IDs.

diff --git a/OvaleAura.lua b/OvaleAura.lua
index b5b96ad..ec2b5fb 100644
--- a/OvaleAura.lua
+++ b/OvaleAura.lua
@@ -95,7 +95,7 @@ end
 function OvaleAura:UNIT_AURA(event, unitId)
 	if unitId == "player" then
 		self:UpdateAuras("player", self.playerGUID)
-	else
+	elseif unitId then
 		self:UpdateAuras(unitId)
 	end
 end