Mattermost integration configuration fails if no commits to repo

Summary

If you try to configure a Mattermost integration for an empty project an error occurs and it's not very informative: Test failed. false.

Steps to reproduce

  • Create a new empty project (don't add issues, commits, anything)
  • Go to Settings -> Integrations
  • Click Mattermost integrations and compile the Webhook field
  • Hit Test settings and save changes

What is the current bug behavior?

The aforementioned error occurs.

What is the expected correct behavior?

It should maybe test the webhook using a standard message (i.e. "Created project xxx") or at least point out the cause for the failing integration (empty project).

Relevant logs and/or screenshots

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