to catch calling params with defaults like "= OUSString()"

Change-Id: Iad060e318ed492c22f8be44e326174fe6d28fff9
Reviewed-on: https://gerrit.libreoffice.org/22932Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>