The problem§

Returning to an old branch may cause the following error:

Fatal error: Type of Class::$isextrafieldmanaged must not be defined (as in class Object) in C:\wamp64\www\dolibarr\htdocs\custom\module\class.class.php on line 0

Correcting the problem§

The simplest solution is to execute the following commands, in the relevant module folder:

git fetch origin
git merge remote/{needed branch}