Stack trace filesizebeat

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x20 pc=0x4664d8]

goroutine 17 [running]:
_/C_/Users/me/Documents/Dev/FileSizeBeat/beat.(*DirSize).WalkFn(0xc08217a480, 0x0, 0x0, 0x0, 0x0, 0x25c0320, 0xc082177560, 0x0, 0x0)
        C:/Users/me/Documents/Dev/FileSizeBeat/beat/filesizebeat.go:113 +0x38
_/C_/Users/me/Documents/Dev/FileSizeBeat/beat.(*DirSize).WalkFn-fm(0x0, 0x0, 0x0, 0x0, 0x25c0320, 0xc082177560, 0x0, 0x0)
        C:/Users/me/Documents/Dev/FileSizeBeat/beat/filesizebeat.go:81 +0x7b
path/filepath.Walk(0x0, 0x0, 0xc08202bcc8, 0x0, 0x0)
        c:/go/src/path/filepath/path.go:394 +0xac
_/C_/Users/me/Documents/Dev/FileSizeBeat/beat.(*FileSizeBeat).Run(0xc0820de140, 0xc0820e6060, 0x0, 0x0)
        C:/Users/me/Documents/Dev/FileSizeBeat/beat/filesizebeat.go:81 +0x2dc
github.com/elastic/beats/libbeat/beat.(*Beat).Run(0xc0820e6060, 0x0, 0x0)
        D:/GoPath/src/github.com/elastic/beats/libbeat/beat/beat.go:246 +0x35a
github.com/elastic/beats/libbeat/beat.(*Beat).Start(0xc0820e6060, 0x0, 0x0)
        D:/GoPath/src/github.com/elastic/beats/libbeat/beat/beat.go:159 +0x116
github.com/elastic/beats/libbeat/beat.Run.func1(0xc0820e6060)
        D:/GoPath/src/github.com/elastic/beats/libbeat/beat/beat.go:107 +0x43
created by github.com/elastic/beats/libbeat/beat.Run
        D:/GoPath/src/github.com/elastic/beats/libbeat/beat/beat.go:119 +0x85

goroutine 1 [chan receive]:
github.com/elastic/beats/libbeat/beat.Run(0x8f2d40, 0xc, 0x8de7f8, 0x5, 0x25c01d8, 0xc0820de140)
        D:/GoPath/src/github.com/elastic/beats/libbeat/beat/beat.go:123 +0xba
main.main()
        C:/Users/me/Documents/Dev/FileSizeBeat/main.go:12 +0xab

goroutine 5 [syscall]:
os/signal.loop()
        c:/go/src/os/signal/signal_unix.go:22 +0x1f
created by os/signal.init.1
        c:/go/src/os/signal/signal_unix.go:28 +0x3e

goroutine 33 [select]:
github.com/elastic/beats/libbeat/publisher.(*messageWorker).run(0xc08219a000)
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/worker.go:61 +0x450
created by github.com/elastic/beats/libbeat/publisher.(*messageWorker).init
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/worker.go:55 +0x125

goroutine 34 [select]:
github.com/elastic/beats/libbeat/publisher.(*messageWorker).run(0xc08219a300)
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/worker.go:61 +0x450
created by github.com/elastic/beats/libbeat/publisher.(*messageWorker).init
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/worker.go:55 +0x125

goroutine 35 [select]:
github.com/elastic/beats/libbeat/publisher.(*bulkWorker).run(0xc0821da000)
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/bulk.go:57 +0x3d1
created by github.com/elastic/beats/libbeat/publisher.newBulkWorker
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/bulk.go:41 +0x211

goroutine 36 [select]:
github.com/elastic/beats/libbeat/publisher.(*bulkWorker).run(0xc0821da070)
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/bulk.go:57 +0x3d1
created by github.com/elastic/beats/libbeat/publisher.newBulkWorker
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/bulk.go:41 +0x211

goroutine 37 [select]:
github.com/elastic/beats/libbeat/publisher.(*messageWorker).run(0xc08218a2a0)
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/worker.go:61 +0x450
created by github.com/elastic/beats/libbeat/publisher.(*messageWorker).init
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/worker.go:55 +0x125

goroutine 38 [select]:
github.com/elastic/beats/libbeat/publisher.(*messageWorker).run(0xc082184390)
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/worker.go:61 +0x450
created by github.com/elastic/beats/libbeat/publisher.(*messageWorker).init
        D:/GoPath/src/github.com/elastic/beats/libbeat/publisher/worker.go:55 +0x125

goroutine 39 [chan receive]:
github.com/elastic/beats/libbeat/service.HandleSignals.func1(0xc08218bbc0, 0xc082180b80, 0xc082180b70)

        D:/GoPath/src/github.com/elastic/beats/libbeat/service/service.go:29 +0x41
created by github.com/elastic/beats/libbeat/service.HandleSignals
        D:/GoPath/src/github.com/elastic/beats/libbeat/service/service.go:32 +0x1ff

goroutine 40 [chan receive]:
github.com/elastic/beats/libbeat/service.(*beatService).Execute(0xb5abd0, 0xc082180c70, 0x1, 0x1, 0xc08218bc80, 0xc08218bce0, 0xb5a300)
        D:/GoPath/src/github.com/elastic/beats/libbeat/service/service_windows.go:21 +0x106
golang.org/x/sys/windows/svc/debug.Run(0xc082002240, 0xc, 0x2604390, 0xb5abd0, 0x0, 0x0)
        D:/GoPath/src/golang.org/x/sys/windows/svc/debug/service.go:40 +0x187
github.com/elastic/beats/libbeat/service.ProcessWindowsControlEvents(0xc082182d00)
        D:/GoPath/src/github.com/elastic/beats/libbeat/service/service_windows.go:55 +0x2c1
created by github.com/elastic/beats/libbeat/service.HandleSignals
        D:/GoPath/src/github.com/elastic/beats/libbeat/service/service.go:38 +0x26d

goroutine 41 [select]:
golang.org/x/sys/windows/svc/debug.Run.func1(0xc08218bd40, 0xc08218bc80, 0xc08218bce0)
        D:/GoPath/src/golang.org/x/sys/windows/svc/debug/service.go:32 +0x165
created by golang.org/x/sys/windows/svc/debug.Run
        D:/GoPath/src/golang.org/x/sys/windows/svc/debug/service.go:38 +0xe9