Fix assembly predicate

src/core/models/assemblies.py

@@ -59,6 +59,8 @@ def is_habitat_manager(user: PlatformUser, assembly: 'Assembly') -> bool:
 def perm_is(permission: str):
     @rules.predicate
     def user_has_permission(user, assembly: 'Assembly'):
+        if assembly is None:
+            return False
         member = ConferenceMember.get_member(conference=assembly.conference, user=user)
         return member.has_perms(permission, require_all=True, require_staff=True)