Add SaveOptional() to save predicates if they exist, and add the

[barakmich]

appropriate test.

[dennwc]

Same as #365 :)

[bobbyrullo]

LGTM, except for that test not passing,and that I am not super familiar with this codebase yet.

[barakmich]

The test isn't passing because something is up on tip.

This is the same as #365. So I'm going to merge #365, and change this to incorporate the additional test.

[bobbyrullo]

👍

[bobbyrullo]

and thanks!