Why am I getting a 500 Internal Server Error trying to set up the Splunk Add-on for Atlassian JIRA Alerts?

I've copied the directory structure to `$SPLUNK_HOME/etc/apps/splunk-add-on-jira-alerts`. I've copied the defaults directory to local. I log in as admin, go to app management, and select Setup on the splunk-add-on-jira-alerts line. This gives me a 500 error (Internal Server error).