Extract `exit_if_no_fallback` function
Extract `exit_if_no_fallback` function

Reviewed By: mroch

Differential Revision: D20285843

fbshipit-source-id: 0cd025b4a1735c5a346575a3964b06cdb146aa50

facebook/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,facebook/flow,mroch/flow,facebook/flow,mroch/flow,mroch/flow,facebook/flow