raise if trying to del a user who can't be deleted

app/models/user.rb

@@ -101,6 +101,10 @@ class User < ApplicationRecord
   end
 
   def delete_and_keep_track_dossiers(administration)
+    if !can_be_deleted?
+      raise "Cannot delete this user because instruction has started for some dossiers"
+    end
+
     if can_be_deleted?
       dossiers.each do |dossier|
         dossier.delete_and_keep_track(administration)