Explicitly specify None cache instead of intentionally omitting it
Explicitly specify None cache instead of intentionally omitting it

Summary: mroch taught me how to correctly pass `None` to optional params in ocaml.

Reviewed By: mroch

Differential Revision: D25655665

fbshipit-source-id: 471603e93bdd1a9f1b864611a8debe0c0b695df1

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