diff --git a/cotisations/models.py b/cotisations/models.py
index 914dc115445919994945b254fd8122934ffff059..9f294f6b5a880049661e0168fb83d3ce876d6334 100644
--- a/cotisations/models.py
+++ b/cotisations/models.py
@@ -194,12 +194,14 @@ class Facture(BaseInvoice):
             return True, None
 
     def can_view(self, user_request, *_args, **_kwargs):
-        if not user_request.has_perm('cotisations.view_facture') and \
-                self.user != user_request:
-            return False, _("You don't have the right to view someone else's "
-                            "invoices history.")
-        elif not self.valid:
-            return False, _("The invoice has been invalidated.")
+        if not user_request.has_perm('cotisations.view_facture'):
+            if self.user != user_request:
+                return False, _("You don't have the right to view someone else's "
+                                "invoices history.")
+            elif not self.valid:
+                return False, _("The invoice has been invalidated.")
+            else:
+                return True, None
         else:
             return True, None
 
diff --git a/machines/models.py b/machines/models.py
index 412e375002eb935087d0ca0c3d9bd91911317cd0..8db0c9d801ed332ce9a74920e8d5ff2060565eec 100644
--- a/machines/models.py
+++ b/machines/models.py
@@ -197,7 +197,11 @@ class Machine(RevMixin, FieldPermissionModelMixin, models.Model):
     def short_name(self):
         """Par defaut, renvoie le nom de la première interface
         de cette machine"""
-        return str(self.interface_set.first().domain.name)
+        interfaces_set = self.interface_set.first()
+        if interfaces_set:
+            return str(interfaces_set.domain.name)
+        else:
+            return "None"
 
     @cached_property
     def complete_name(self):
diff --git a/users/models.py b/users/models.py
index c204f763e193a7a391864787aa00824febe83967..928e771f6810e84476f42e60b0fd00ae03988fc2 100755
--- a/users/models.py
+++ b/users/models.py
@@ -845,8 +845,7 @@ class User(RevMixin, FieldPermissionModelMixin, AbstractBaseUser,
         """
         return user_request == self, None
 
-    @staticmethod
-    def can_change_room(user_request, *_args, **_kwargs):
+    def can_change_room(self, user_request, *_args, **_kwargs):
         """ Check if a user can change a room
 
         :param user_request: The user who request