Cancelling a task group with no tasks throws a 404
If a task group such as applicability generation has no tasks, it throws an error. This is incredibly confusing to the point that i thought i was doing something wrong. A user would not expect that when given a task group id, canceling that task group would throw a 404.
To reproduce, generate applicability for a repository with no bound consumers, grab the task id, and attempt to cancel it.