How do I find which entry the sync error is related to? Not obvious in error detail.

Value cannot be null.
Parameter name: path

Action: SyncCalendarList

System.ArgumentNullException: Value cannot be null.
Parameter name: path
at Foundation.NSBundle.FromPath (System.String path) [0x00009] in <115d6af1f8fd488faf437fb0c661ce0f>:0
at XCalendarApp.Common.Mac.Localization.XLocalization.GetStringForLanguage (System.String language, System.String identifier) [0x00010] in <2f11d031955b47acb7e7073c569e2e5e>:0
at XCalendarApp.Common.Localization.Localizer.GetStringForLanguage (System.String language, System.String identifier) [0x00005] in <bf9ec3e54c4249ec953e8d886508bb2c>:0
at XCalendarApp.ProviderBase.AccountProviderBase`8[TCachedCalendar,TProviderCalendarItem,TCachedAppointment,TProviderAppointmentItem,TCachedContacts,TCachedContact,TProviderContactItem,TAppointmentDbData].GetCalendarCategoryIDFromName (System.String calendarName) [0x0001b] in <73e54dccd14a4dd28e845c5377a70ffa>:0
at XCalendarApp.GoogleProvider.GoogleAccount.GetProviderCalendarList () [0x0010b] in <81e09bb6a9fd48b6931061d103ec2595>:0
at XCalendarApp.ProviderBase.AccountProviderBase`8[TCachedCalendar,TProviderCalendarItem,TCachedAppointment,TProviderAppointmentItem,TCachedContacts,TCachedContact,TProviderContactItem,TAppointmentDbData].SyncCalendarList () [0x0008c] in <73e54dccd14a4dd28e845c5377a70ffa>:0