Don't upsync empty contact tags

* EAS 12.0/12.1 don't mind these, but EAS 2.5 objects in some cases
  (title and prefix, certainly)  and the upsync fails
* The error case occurs because the ContentValues provided by
  ContactsProvider actually has a value; the value, however, is an
  empty string
* Prevent this by checking for empty values before serializing

Bug: 2607778
Change-Id: I853ce711024a414f53861720000cc87a7349d660
1 file changed