Disappeared Holidays Calendar
When I opened my Calendar app, I saw a "!" next to my Holiday calendar (FI Holidays since I'm Finnish). Well, I unchecked it and when I was about to check it on again in Calendar preferences, the calendar won't show up again in the sidebar (There's only On my Mac- calendar and Birthday calendar).
It has just disappeared completely. I even looked in my Library for the calendar, but it isn't there anymore with the events.
What can I do? Why did it went away?
MacBook Air, macOS Sierra (10.12.3)