api: set event_types to empty list if not supplied in register.
Previously, if you didn't specify a list of `event_types` in either `register` or `call_on_each_event`, you'd get an exception due to the invalid event format.
This fixes
@@ -616,6 +616,9 @@ class Client(object):
if narrow is None:
narrow = []
+ if event_types is None:
+ event_types = []
+
request = dict(
event_types=event_types,
narrow=narrow,
