Contact: allow the contacts store to be null
We need to know about the primary store in a Contacts.Contact
for 2
reasons:
- To find out which persona is the "primary" persona (if there is one)
- To save any new properties (which are not linked to a persona) in the primary store
However, in some cases we do not have a special need for these 2
properties: in unit tests, and when we want to port our
(de-)serialization code to work with an array of Contacts.Contact
objects (especially with the importer being in a separate process).
In those cases, it should be allowed to pass null
instead.