fix: Return None if Nodestore event is not yet in Snuba (#16422)
fix: Return None if Nodestore event is not yet in Snuba (#16422)

Since events are written into Nodestore before Snuba, just return None
if a requested event has not made it all the way into Snuba yet.

This can come up on the embedded error page where user feedback can be
submitted before the event makes it all the way through.

Fixes SENTRY-E59
beeftornado/sentry,beeftornado/sentry,beeftornado/sentry