panic: interface conversion: interface {} is nil, not string

github.com/syncthing/syncthing/lib/ur/failurereporting.go in serve at line 97

    			}
    			url = opts.CRURL + "/failure"
    		case e := <-h.evChan:
    			descr := e.Data.(string)
    			if stat, ok := h.buf[descr]; ok {
    				stat.last = e.Time
    				stat.count++

github.com/syncthing/syncthing/lib/util/utils.go in Serve at line 300
github.com/thejerf/suture@v3.0.2+incompatible/supervisor.go in func1 at line 600