Thanks, this E_NOTICE has been fixed in the next release. It occurred when changing the BB-Code on an existing prefix so that it no longer has a BB-Code, but the existing BB-Code on the prefix did not represent a real BB-Code.
One way to create this situation is to delete a prefix BB-Code while the add-on is disabled, then enable the add-on and delete the prefix too. In 4.0.8, this case will no longer log the E_NOTICE.