The = None (or null) pattern is a Java convention, its not needed in Python.

Change-Id: I0041d4030db05234eeefc8606f571da38174f962
Reviewed-on: https://gerrit.libreoffice.org/23669
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>