AutocompleteController#merge_request_target_branches generates a 500 error after 15s timeout
Making a request to
/autocomplete/merge_request_target_branches.json without parameters, happens frequently on GitLab.com (most likely by crawlers, etc) and results in a 500 error after a 15 second timeout.
Here are some examples of this from the logs: https://log.gitlab.net/goto/9b18672786687390c5277a5efdc0856e
Reported in #mech_symp_alerts