Stop trying to fetch events with event_id=None. (#5753)

`None` is not a valid event id, so queuing up a database fetch for it seems
like a silly thing to do.

I considered making `get_event` return `None` if `event_id is None`, but then
its interaction with `allow_none` seemed uninituitive, and strong typing ftw.

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.d/5753.misc b/changelog.d/5753.misc
new file mode 100644
index 0000000000..22bba9ce3c
--- /dev/null
+++ b/changelog.d/5753.misc
@@ -0,0 +1 @@
+Stop trying to fetch events with event_id=None.