Domain Mapping PHP Notice "Trying to get property of non-object"

Hi - we are starting to get a lot of PHP notices in our logs that say the following:

PHP Notice: Trying to get property of non-object in /var/app/current/wp-content/plugins/domain-mapping/classes/Domainmap/Module/Mapping.php on line 1019

We are currently running verson 4.4.2.0 because 4.4.2.1 caused major CPU issues and 4.4.2.3 seems to have caused some sites to break (based on the support threads here) so we are reluctant to update. Any ideas why we'd be getting these notices?

Thanks