IE Error when clicking on/resizing an event using Warmup/Cool down Areas

In Internet explorer 11, when clicking or resizing the event in the following demo: https://demos.daypilot.org/javascript-scheduler-warmup-cooldown/

the following error occurs:
SCRIPT5007: Unable to get property '0' of undefined or null reference

I also have the same issue in my code, which is based on this example: https://code.daypilot.org/82331/javascript-scheduler-warm-up-and-cool-down-time

Are there any work arounds or other settings I need to apply in order to not get this error in IE?

Thanks

Stew.