Add annotations to mark API calls as being private.
fix comment
default the stale value to CBLStaleNever (otherwise, defaults to null)
Change from %@ -> %s (as found in https://github.com/couchbase/couchbase-lite-android-core/pull/6)
Add defensive null checking  (as found in https://github.com/couchbase/couchbase-lite-android-core/pull/6)