We filter out hidden comments out of Issue descriptions but this
breaks when description is null (which is unusual). So this commit
just checks to see if the description is None and if so, not to
filter anything out.
Such payloads are generated when a GitLab repository has merge
request approvals enabled and a project member approves a merge
request. Approving is not the same as merging.
Payloads that don't have a payload['object_attributes']['action']
attribute are generated when GitLab sends a test payload to verify
if the webhook was set up successfully. In this case, we should
send a message notifying that the webhook was configured
successfully.
All webhook fixtures in zerver/fixtures/<webhook_name> have now
been moved to dedicated webhook-specific directories under
zerver/webhooks/<webhook_name>/fixtures, where <webhook_name> is
the name of the webhook.