fix date_expiration

app/views/users.py

@@ -397,9 +397,12 @@ def create_user_form(REQUEST, user_name=None, edit=0):
                 del vals["status"]  # no one can't change its own status
             if "date_expiration" in vals:
                 try:
+                    if vals["date_expiration"]:
                         vals["date_expiration"] = datetime.datetime.strptime(
                             vals["date_expiration"], "%d/%m/%Y"
                         )
+                    else:
+                        vals["date_expiration"] = None
                 except ValueError:
                     H.append(tf_error_message("date expiration invalide"))
                     return "\n".join(H) + "\n" + tf[1] + F