[native] Make it possible for coolOrNerdMode/keyserverURL to be set to null/undefined

Summary:
This makes the following diff a little bit easier, and is otherwise not a significant change.

These two lines in the following diff are the reason that this diff is necessary.

Test Plan: Flow

Reviewers: inka

Reviewed By: inka

Subscribers: tomek, varun

Differential Revision: https://phab.comm.dev/D12018