Error: Unable to process file command 'output' successfully

[BartSchuurmans]

Describe the bug
When using actions/github-script@v8, I call core.setOutput('foo', '<uri starting with digits here>') and get the following error:

Error: Unable to process file command 'output' successfully.
Error: Invalid format '<<ghadelimiter_8bdc70d4-e393-4f93-a66b-55143a8a079f'. Name must not be empty and delimiter must not be empty

I have also encountered this error when not setting any output myself.

Screenshots

[BartSchuurmans]

Nevermind, turns out this happens because I called core.setOutput('', undefined). The error could be better though.