As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING GROUND HANDLING OF FLIGHT 6128 TO BOS CREW RECEIVED LAVATORY SMOKE CAUTION MESSAGE WITH NO EVIDENCE OF SMOKE. THE SMOKE DETECTOR WAS DETERMINED TO BE FAULTY AND WAS REPLACED IN BOS. A SATISFACTORY OPERATIONAL CHECK WAS PERFORMED AND AIRCRAFT WAS RELEASED FOR SERVICE.