Don't give a conflict resolver an empty base revision
Don't give a conflict resolver an empty base revision

If the base revision's body isn't available anymore (we try to avoid it
but it can happen), pass a nil document to the resolver instead of an
object with no properties.

couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios