Plugins/slack: commit author shown empty

A collaborator’s username shown as empty in the slack notification when the git commit is registered with an email not known to github:
All the while, the web ui (build available publicly here) displays the nickname correctly.

Both notifications and web ui info are always shown correctly users when the git commit author’s email matches their github account email.

While the issue could probably be solved by registering the git email address with github, it’s still strange (and looks like a bug) that the the slack notification is broken even when the web ui is able to display the nickname correctly.

Setup details

Only tested with GitHub.

Full .drone.yml available here.

In a self-hosted dockerized deployment. From docker image ls:

REPOSITORY                         TAG                                    IMAGE ID       CREATED        SIZE
drone/drone-runner-docker          1                                      42f73cc80149   8 weeks ago    25.7MB
plugins/slack                      latest                                 6bc5512817c3   8 weeks ago    11.1MB
drone/drone                        2                                      22e072ad33e1   2 months ago   60.3MB