'Export and import a single AssetMetadata to XML with a None created_by field, without causing an exception.'

def test_export_with_None_value(self):

    asset_md = AssetMetadata(self.course_id.make_asset_key('asset', 'none_value'), created_by=None)
    asset = etree.Element('asset')
    asset_md.to_xml(asset)
    asset_md.from_xml(asset)
