Keep spinning when function return value is null

[Sanya-L]

Hi, here is the situation I'm trying to work on: I will call a function to get the index number(where I want to stop), but in the meantime, if the return value is empty the wheel will keep spinning. Is that any similar feature existing?

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[kevlatus]

relates to #91