sefaira/rho-contracts.js — pull request #7 by jake-miles (2014-04-02 15:34:56+00:00)
Title: adds orNull to a contract, allowing a specific contract to specify that ...

...one of its accepted values is null, instead of hard-coding this definition of a missing value.

I took a stab at this. What do we think of this approach? i.e. let the contract define isMissing, and orNull lets you specify that a particular contract also allows null.

@gmarceau @jonahkagan