Use default site per default

favicon/models.py

@@ -41,7 +41,7 @@ class Favicon(models.Model):
     on_site = objects
 
     if use_sites:
-        site = models.ForeignKey(Site, related_name="favicon", on_delete=models.CASCADE, blank=True, null=True)
+        site = models.ForeignKey(Site, related_name="favicon", on_delete=models.CASCADE, blank=True, null=True, default=settings.SITE_ID)
 
         on_site = CurrentSiteManager()