Event conflict endpoint returns Server error 500
Steps to reproduce
When you schedule a multiple event, the conflict check admin-ng/event/new/conflicts fails and returns a 500 Server error. The event get created but the notification says that they are failed.
The problem is that the property "capture.device.timezone" is not returned by some capture agent. Therefore we get here a null pointer exception.
The server timezone should be used as default with a warning log message if the capture agent timezone is not set.