diff --git a/app/auth/models.py b/app/auth/models.py
index 20149e14a..dc9e32fc7 100644
--- a/app/auth/models.py
+++ b/app/auth/models.py
@@ -302,6 +302,10 @@ class User(UserMixin, db.Model, ScoDocModel):
             if field in args:
                 args[field] = args[field] or ""
 
+        # chaines ne devant pas être vides mais au contraire null (unicité)
+        if "cas_id" in args:
+            args["cas_id"] = args["cas_id"] or None
+
         return args_dict
 
     def from_dict(self, data: dict, new_user=False):
@@ -333,7 +337,7 @@ class User(UserMixin, db.Model, ScoDocModel):
         exp = ScoDocSiteConfig.get("cas_uid_from_mail_regexp")
         if exp and self.email_institutionnel:
             cas_id = ScoDocSiteConfig.extract_cas_id(self.email_institutionnel)
-            if cas_id is not None:
+            if cas_id:
                 self.cas_id = cas_id
 
     def get_token(self, expires_in=3600):