Panic in Defender service

[ghost]

Defender log

2018/06/06 09:47:36 execute http request: Delete http://moon:4444/wd/hub/session/chrome-65-0-d6e16aee-2122-4568-b85e-2a7062e39d5b: context deadline exceeded
2018/06/06 09:47:36 http: proxy error: context canceled
2018/06/06 09:47:40 http: panic serving 192.168.13.1:47142: close of closed channel
goroutine 37 [running]:
net/http.(*conn).serve.func1(0xc42012e1e0)
	/usr/local/go/src/net/http/server.go:1697 +0xd0
panic(0x67ee80, 0x705bd0)
	/usr/local/go/src/runtime/panic.go:491 +0x283
main.(*Expiration).On(0x849cb0, 0xdf8475800, 0x6e48b8)
	/go/src/github.com/aandryashin/moon/cmd/defender/defender.go:149 +0x110
main.mux.func3(0xc42049c200)
	/go/src/github.com/aandryashin/moon/cmd/defender/defender.go:124 +0xe9
net/http/httputil.(*ReverseProxy).ServeHTTP(0xc42004e5c0, 0x816f80, 0xc42049e0e0, 0xc42049c100)
	/usr/local/go/src/net/http/httputil/reverseproxy.go:169 +0x17c
net/http.(*ServeMux).ServeHTTP(0xc42000f3e0, 0x816f80, 0xc42049e0e0, 0xc42049c100)
	/usr/local/go/src/net/http/server.go:2254 +0x130
net/http.serverHandler.ServeHTTP(0xc420120340, 0x816f80, 0xc42049e0e0, 0xc42049c100)
	/usr/local/go/src/net/http/server.go:2619 +0xb4
net/http.(*conn).serve(0xc42012e1e0, 0x817440, 0xc42004e640)
	/usr/local/go/src/net/http/server.go:1801 +0x71d
created by net/http.(*Server).Serve
	/usr/local/go/src/net/http/server.go:2720 +0x288

and so on

2018/06/06 09:47:40 http: panic serving 192.168.13.1:49076: close of closed channel
goroutine 4789 [running]:
net/http.(*conn).serve.func1(0xc42041a000)
	/usr/local/go/src/net/http/server.go:1697 +0xd0
panic(0x67ee80, 0x705bd0)
	/usr/local/go/src/runtime/panic.go:491 +0x283
main.(*Expiration).On(0x849cb0, 0xdf8475800, 0x6e48b8)
	/go/src/github.com/aandryashin/moon/cmd/defender/defender.go:149 +0x110
main.mux.func3(0xc42016e100)
	/go/src/github.com/aandryashin/moon/cmd/defender/defender.go:124 +0xe9
net/http/httputil.(*ReverseProxy).ServeHTTP(0xc42004e5c0, 0x816f80, 0xc4203da000, 0xc42016e000)
	/usr/local/go/src/net/http/httputil/reverseproxy.go:169 +0x17c
net/http.(*ServeMux).ServeHTTP(0xc42000f3e0, 0x816f80, 0xc4203da000, 0xc42016e000)
	/usr/local/go/src/net/http/server.go:2254 +0x130
net/http.serverHandler.ServeHTTP(0xc420120340, 0x816f80, 0xc4203da000, 0xc42016e000)
	/usr/local/go/src/net/http/server.go:2619 +0xb4
net/http.(*conn).serve(0xc42041a000, 0x817440, 0xc4201ce080)
	/usr/local/go/src/net/http/server.go:1801 +0x71d
created by net/http.(*Server).Serve
	/usr/local/go/src/net/http/server.go:2720 +0x288
2018/06/06 09:47:50 http: panic serving 192.168.13.1:49158: close of closed channel
goroutine 4777 [running]:
net/http.(*conn).serve.func1(0xc4204ee140)
	/usr/local/go/src/net/http/server.go:1697 +0xd0
panic(0x67ee80, 0x705bd0)
	/usr/local/go/src/runtime/panic.go:491 +0x283
main.(*Expiration).On(0x849cb0, 0xdf8475800, 0x6e48b8)
	/go/src/github.com/aandryashin/moon/cmd/defender/defender.go:149 +0x110
main.mux.func3(0xc42032c300)
	/go/src/github.com/aandryashin/moon/cmd/defender/defender.go:124 +0xe9
net/http/httputil.(*ReverseProxy).ServeHTTP(0xc42004e5c0, 0x816f80, 0xc4204e6000, 0xc42032c200)
	/usr/local/go/src/net/http/httputil/reverseproxy.go:169 +0x17c
net/http.(*ServeMux).ServeHTTP(0xc42000f3e0, 0x816f80, 0xc4204e6000, 0xc42032c200)
	/usr/local/go/src/net/http/server.go:2254 +0x130
net/http.serverHandler.ServeHTTP(0xc420120340, 0x816f80, 0xc4204e6000, 0xc42032c200)
	/usr/local/go/src/net/http/server.go:2619 +0xb4
net/http.(*conn).serve(0xc4204ee140, 0x817440, 0xc42009a600)
	/usr/local/go/src/net/http/server.go:1801 +0x71d
created by net/http.(*Server).Serve
	/usr/local/go/src/net/http/server.go:2720 +0x288

Full log https://pastebin.com/ZRuDEvuq