Error running `melody install`

[mapaiva]

I already have a repository with a properly Melody.toml and Melody.lock and I've been using it without any issues. But turns out that today I ran a melody install and got this error.

melody install
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x5092dc]

goroutine 1 [running]:
panic(0x89e9e0, 0xc420012110)
	/usr/share/go/src/runtime/panic.go:500 +0x1a1
github.com/mdy/melody/resolver.DecodeGraph.func1(0xc42017b1e0, 0xc42014acd0, 0xc42015a901, 0x0, 0xc42015a930)
	/home/matheus/goworkspace/src/github.com/mdy/melody/resolver/encode.go:79 +0x11c
github.com/mdy/melody/resolver.DecodeGraph(0xb02ae0, 0xc420109060, 0xb07ba0, 0xc4200fe4e0, 0x0)
	/home/matheus/goworkspace/src/github.com/mdy/melody/resolver/encode.go:102 +0x4dd
github.com/mdy/melody/project.(*Project).LoadLockfile(0xc42009a800, 0xc42001cdc0, 0x47, 0xc42001cdc0, 0x47)
	/home/matheus/goworkspace/src/github.com/mdy/melody/project/lockfile.go:30 +0x195
github.com/mdy/melody/project.Load(0xc420016104, 0x3b, 0xc4200516c8, 0x1, 0x1)
	/home/matheus/goworkspace/src/github.com/mdy/melody/project/config.go:54 +0x3f9
github.com/mdy/melody/cli.runInstall(0xc420016104, 0x3b, 0x0, 0x0, 0x4)
	/home/matheus/goworkspace/src/github.com/mdy/melody/cli/install.go:24 +0x4d
github.com/mdy/melody/cli.install(0xc42001b540, 0x0, 0xc42001b540)
	/home/matheus/goworkspace/src/github.com/mdy/melody/cli/install.go:18 +0xfb
github.com/urfave/cli.HandleAction(0x889640, 0x94bd30, 0xc42001b540, 0xc420014a00, 0x0)
	/home/matheus/goworkspace/src/github.com/urfave/cli/app.go:485 +0xd4
github.com/urfave/cli.Command.Run(0x912cd1, 0x7, 0x91119d, 0x1, 0x0, 0x0, 0x0, 0x917f9e, 0x14, 0x0, ...)
	/home/matheus/goworkspace/src/github.com/urfave/cli/command.go:207 +0xb96
github.com/urfave/cli.(*App).Run(0xc42008d380, 0xc42000c480, 0x2, 0x2, 0x0, 0x0)
	/home/matheus/goworkspace/src/github.com/urfave/cli/app.go:250 +0x812
github.com/mdy/melody/cli.Main(0x913659, 0x9)
	/home/matheus/goworkspace/src/github.com/mdy/melody/cli/cli.go:48 +0x32f
main.main()
	/home/matheus/goworkspace/src/github.com/mdy/melody/main.go:10 +0x39

I'm on Linux. Disto: Ubuntu 16.04 Arch: x86_64

Any ideas about what could trigger this?