user_display_name_cache = {} if user_display_name_cache.nil?
- if user_display_name_cache and user_display_name_cache[self.user_id]
+ if user_display_name_cache and user_display_name_cache.key?(self.user_id)
# use the cache if available
elsif self.user.data_public?
user_display_name_cache[self.user_id] = self.user.display_name