null pointer error when using websockets

[ohnorobo]

When getting started building ss-server I found this behavior

To reproduce

go run ./cmd/outline-ss-server -config=./cmd/outline-ss-server/config_example.yml

Then just from the browser hit either
http://127.0.0.1:8000/SECRET/udp or http://127.0.0.1:8000/SECRET/tcp

result

Feb 17 17:24:47.071 ERR failed to upgrade err="websocket: the client is not using the websocket protocol: 'upgrade' token not found in 'Connection' header"
Feb 17 17:24:47.071 INF http: panic serving 127.0.0.1:61625: runtime error: invalid memory address or nil pointer dereference
goroutine 4 [running]:
net/http.(*conn).serve.func1()
	/usr/local/go/src/net/http/server.go:1947 +0xb0
panic({0x1027afa60?, 0x102b186b0?})
	/usr/local/go/src/runtime/panic.go:785 +0x124
main.(*OutlineServer).runConfig.func1.2.7({0x102843370?, 0x1400013c0e0?}, 0x1400013a140)
	/Users/2385180/Projects/outline-ss-server/cmd/outline-ss-server/main.go:348 +0xd8
net/http.HandlerFunc.ServeHTTP(0x1400013a140?, {0x102843370?, 0x1400013c0e0?}, 0x0?)
	/usr/local/go/src/net/http/server.go:2220 +0x38
main.(*OutlineServer).runConfig.func1.2.ProxyHeaders.21({0x102843370, 0x1400013c0e0}, 0x1400013a140)
	/Users/2385180/go/pkg/mod/github.com/gorilla/handlers@v0.0.0-20150720190736-60c7bfde3e33/proxy_headers.go:54 +0xc8
net/http.HandlerFunc.ServeHTTP(0x0?, {0x102843370?, 0x1400013c0e0?}, 0xb?)
	/usr/local/go/src/net/http/server.go:2220 +0x38
main.(*OutlineServer).runConfig.func1.2.StripPrefix.22({0x102843370, 0x1400013c0e0}, 0x1400013a000)
	/usr/local/go/src/net/http/server.go:2282 +0x228
net/http.HandlerFunc.ServeHTTP(0x140002dc000?, {0x102843370?, 0x1400013c0e0?}, 0x102573094?)
	/usr/local/go/src/net/http/server.go:2220 +0x38
net/http.(*ServeMux).ServeHTTP(0x0?, {0x102843370, 0x1400013c0e0}, 0x1400013a000)
	/usr/local/go/src/net/http/server.go:2747 +0x1b4
net/http.serverHandler.ServeHTTP({0x14000114ff0?}, {0x102843370?, 0x1400013c0e0?}, 0x6?)
	/usr/local/go/src/net/http/server.go:3210 +0xbc
net/http.(*conn).serve(0x1400012c090, {0x102843e08, 0x1400024fd10})
	/usr/local/go/src/net/http/server.go:2092 +0x4fc
created by net/http.(*Server).Serve in goroutine 51
	/usr/local/go/src/net/http/server.go:3360 +0x3dc

[ohnorobo]

Related to the ongoing work in #228

[ohnorobo]

for the record I'm synced at 35fc25e