plugin XEP-0363: fix handling of empty upload_jid in _get_slot

libervia/backend/plugins/plugin_xep_0363.py

@@ -300,7 +300,8 @@ class XEP_0363:
         client = self.host.get_client(profile_key)
         filename = filename.replace("/", "_")
         d = defer.ensureDeferred(self.get_slot(
-            client, filename, size, content_type or None, jid.JID(upload_jid) or None
+            client, filename, size, content_type or None,
+            jid.JID(upload_jid) if upload_jid else None
         ))
         d.addCallback(lambda slot: (slot.get, slot.put, slot.headers))
         return d