Fix error problem when array returns nil

Author: ishikawa999

app/models/custom_message_setting.rb

@@ -26,7 +26,7 @@ def custom_messages_with_timestamp(lang)
   def latest_messages_applied?(lang)
     return true if self.new_record?
 
-    redmine_message_customize_timestamp = I18n.backend.send(:translations)[:"#{lang}"][:redmine_message_customize_timestamp]
+    redmine_message_customize_timestamp = I18n.backend.send(:translations)[:"#{lang}"]&.[](:redmine_message_customize_timestamp)
     redmine_message_customize_timestamp == self.updated_on.to_i.to_s
   end