It must return a reference to a freshly created object that should be populated with the validated form data. It receives a reference to the controller instance calling it.
If the callback is unable to create an empty object for whatever reason, you should throw midcom_error. There is no error handling whatsoever on the side of the controller instance. If the function returns, a valid instance is expected.
\midcom_helper_datamanager2_controller_create&$controller The current controller
\midcom_core_dbaobjectThe newly-created object