Property of 'slug' undefined.

[TheMerphin]

If you are starting from scratch in the content/events folder the following error occurs:

To reproduce this bug, proceed as follows:

Move every event except one of the events folder somewhere else, so that only one event is left in that folder.
Now run the application and the error should occur.

Current workaround is to not start from scratch adding new events, but adding events to the existing ones and after that remove all unnecessary ones.