After upgrading to Sabre VObject3 in T48, new packages are required.
Use git master head from rRPK at 6effb4c9c3.
Sabre VObject 3 is not part of the git source tree anymore. Dependencies are listed in plugins/libcalendaring/composer.json and need to be installed in the main product (e.g. roundcubemail, iRony or freebusy) where a composer autoloader is used.