13.0p and Calendar - Cannot set properties of null on endLeftOffset

[itb]

While upgrading to 13.0p I get an error on existing code (that worked in 12) in the ISC_Calendar code. My code tries to put a timeline without events on a tab of a tabset. After this error, rendering of the rest of the application is broken: selecting another tab shows an empty tab. Any hints on how to prevent the error that endField is null?

Cannot set properties of null (setting 'endLeftOffset')
Stack from error.stack:
    TimelineView.buildSnapGapList(<no args: exited>) on [TimelineView ID:isc_Timeline_0_timelineView] @ ISC_Calendar.js:411:27
    TimelineView._rebuildFields(<no args: exited>) on [TimelineView ID:isc_Timeline_0_timelineView] @ ISC_Calendar.js:412:349
    TimelineView._rebuild(<no args: exited>) on [TimelineView ID:isc_Timeline_0_timelineView] @ ISC_Calendar.js:412:768
    TimelineView.setTimelineRange(<no args: exited>) on [TimelineView ID:isc_Timeline_0_timelineView] @ ISC_Calendar.js:424:256
    TimelineView.setChosenDate(<no args: exited>) on [TimelineView ID:isc_Timeline_0_timelineView] @ ISC_Calendar.js:355:83
    Calendar.setChosenDate(<no args: exited>) on [Timeline ID:isc_Timeline_0] @ ISC_Calendar.js:616:399
    Calendar.draw(<no args: exited>) on [Timeline ID:isc_Timeline_0] @ ISC_Calendar.js:625:41
    Layout.layoutChildren(<no args: exited>) on [VLayout ID:isc_ChartererScheduleView_0] @ ISC_Foundation.js:344:264

[Isomorphic]

Please show the setup for your Timeline - no need to include data or DataSources right now.