diff --git a/stateless_uptime_kuma/uptime_kuma.py b/stateless_uptime_kuma/uptime_kuma.py
index d156fd0..742b385 100644
--- a/stateless_uptime_kuma/uptime_kuma.py
+++ b/stateless_uptime_kuma/uptime_kuma.py
@@ -140,7 +140,7 @@ class Monitor(Item):
             for t, v in self.tags:
                 if (t.id, v) not in current_tags:
                     logger.debug(f"Adding tag: '{t}, {v}'")
-                    self.api.add_monitor_tag(tag_id=t.id, monitor_id=self.id, value=v)
+                    self.api.add_monitor_tag(tag_id=t.id, monitor_id=self.id, value=v if v is not None else "")
         self.saved = True
 
     def __repr__(self):