generator: Use empty string instead of None
generator: Use empty string instead of None

for better type checking: both are bool()==False, but None is not str.

Signed-off-by: Philipp Hahn <8cb7a2c205789112a9f61bc3102305826b6a8db1@univention.de>

libvirt/libvirt-python,libvirt/libvirt-python,libvirt/libvirt-python