Handle zero meetings correctly

bbbmon/bbbmon.py

@@ -133,6 +133,10 @@ def get_meetings(secret: Secret, bbb_url: Url) -> Iterable[XmlDictConfig]:
     meetings = []
     d = request_meetings(secret, bbb_url)
 
+    if d["meetings"] is None:
+        print("There are no active meetings currently.")
+        exit()
+
     if type(d["meetings"]["meeting"]) is XmlListConfig:
         meetings = sorted([m for m in d["meetings"]["meeting"] if m["running"] == "true"], key=lambda x:int(x['participantCount']), reverse=True)
     elif type(d["meetings"]["meeting"]) is XmlDictConfig: