change this parameter in the default.xml file <entry key='web.persistSession'>false</entry>
and restart traccar
I changed the datatype to medium blob and the error no longer appears in the logs. Useful if you still want to persist user sessions. If not, then disabling it as you say is the best option.
I've just had the same error. It seems to be coming from the map column in JettySessions table. It's currently set as blob type. I'll change it to medium blob and see if it fixes the issue and report back here