added unit test for the optional fields in the SwiftDocument, while parsing on collection updates 
added unit test for the optional fields in the SwiftDocument, while parsing on collection updates 

Duckr/SwiftDDP,infinitedg/SwiftDDP,siegesmund/SwiftDDP,infinitedg/SwiftDDP,siegesmund/SwiftDDP,Duckr/SwiftDDP,mjgaylord/SwiftDDP,mjgaylord/SwiftDDP