Undefined property: stdClass::$menu in workbench_access_node_presave() [closed]

Question

I'm logged in as user/1 and am using a workbench module. Whenever I unpublish a published revision (using the moderate tab) I am presented with the following errors:

Notice: Undefined property: stdClass::$menu in workbench_access_node_presave() (line 667 of /home/mysite/public_html/sites/all/modules/workbench_access/workbench_access.module).
Notice: Undefined property: stdClass::$menu in workbench_access_node_presave() (line 668 of /home/mysite/public_html/sites/all/modules/workbench_access/workbench_access.module).
Notice: Undefined property: stdClass::$menu in workbench_access_node_presave() (line 667 of /home/mysite/public_html/sites/all/modules/workbench_access/workbench_access.module).
Notice: Undefined property: stdClass::$menu in workbench_access_node_presave() (line 668 of /home/mysite/public_html/sites/all/modules/workbench_access/workbench_access.module).

There is a green tick next to - The live revision of this content has been unpublished. and then there is a Warning message as well: Currently there is no published revision of this node.

How do I prevent these messages from appearing? What am I doing wrong?