Weird SEGV on shutdown

[chrko]

Mar 30 14:59:59 eris systemd[1]: Stopping frank (robust irc-bot)...
Mar 30 14:59:59 eris frank[22705]: 2019/03/30 14:59:59 Exiting due to signal "terminated"
Mar 30 14:59:59 eris frank[22705]: 2019/03/30 14:59:59 Deleting Session. Goodbye.
Mar 30 14:59:59 eris frank[22705]: panic: runtime error: invalid memory address or nil pointer dereference
Mar 30 14:59:59 eris frank[22705]: [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x7f9b68]
Mar 30 14:59:59 eris frank[22705]: goroutine 177463 [running]:
Mar 30 14:59:59 eris frank[22705]: main.Nick(...)
Mar 30 14:59:59 eris frank[22705]:         […]/gocode/src/github.com/nnev/frank/tools.go:43
Mar 30 14:59:59 eris frank[22705]: main.runnerGreet(0xc000429560, 0xc000550f98, 0xc0001fcf90)
Mar 30 14:59:59 eris frank[22705]:         […]/gocode/src/github.com/nnev/frank/greet.go:49 +0x58
Mar 30 14:59:59 eris frank[22705]: main.listenersRun.func1(0xc000000008, 0x9280f8)
Mar 30 14:59:59 eris frank[22705]:         […]/gocode/src/github.com/nnev/frank/listeners.go:36 +0x32
Mar 30 14:59:59 eris frank[22705]: golang.org/x/sync/errgroup.(*Group).Go.func1(0xc000429590, 0xc0003cffc0)
Mar 30 14:59:59 eris frank[22705]:         […]/gocode/src/golang.org/x/sync/errgroup/errgroup.go:57 +0x57
Mar 30 14:59:59 eris frank[22705]: created by golang.org/x/sync/errgroup.(*Group).Go
Mar 30 14:59:59 eris frank[22705]:         […]/gocode/src/golang.org/x/sync/errgroup/errgroup.go:54 +0x66
Mar 30 14:59:59 eris systemd[1]: frank_robust.service: Main process exited, code=exited, status=2/INVALIDARGUMENT
Mar 30 14:59:59 eris systemd[1]: frank_robust.service: Failed with result 'exit-code'.
Mar 30 14:59:59 eris systemd[1]: Stopped frank (robust irc-bot).