SIGSEGV server.go on build, in build stage, running tests

[Karm]

Submitted by @robcza

2018/12/05 18:21:56 There is no hash on path test-data/400_resolver_cache.bin.md5 ready for client CommonName 400. Although data file on path test-data/400_resolver_cache.bin exists. Client sent away.
2018/12/05 18:21:56 interrupt
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x6c7427]

goroutine 1592 [running]:
net/http.(*Server).Shutdown(0xc0000120d0, 0x0, 0x0, 0x0, 0x0)
    /opt/go/src/net/http/server.go:2620 +0x167
github.com/Karm/serve-file.main.func2(0xc0000843c0, 0xc0000120d0, 0xc000708070, 0xc0000120d0)
    /gopath/src/github.com/Karm/serve-file/server.go:174 +0x9c
created by github.com/Karm/serve-file.main
    /gopath/src/github.com/Karm/serve-file/server.go:171 +0x2d0
exit status 2
FAIL    github.com/Karm/serve-file    26.618s
The command '/bin/sh -c go test' returned a non-zero code: 1