ArmA 3 Campaign description.ext

This following inside every mission class is not necessary:

briefingName = "Mission Name";
author = "Snake Man";
overviewText = "Campaign mission overview";

Because these values are read from the mission description.ext instead.

When you are creating your ArmA 3 campaign and if you get this error:

Warning Message: No entry 'Campaigns\<NAME>\description.ext/Campaign.briefingName'.

You need to add one line in description.ext file:

briefingName = "My Campaign!";

And its fixed.