nil pointer dereference accessing account webhooks

[weppos]

I found the issue while tracking back several exceptions happening in strillone.

Here's the error in strillone:

2019-06-13T07:59:36.100612+00:00 app[web.1]: 2019/06/13 07:59:36 http: panic serving 10.33.137.185:11287: runtime error: invalid memory address or nil pointer dereference
2019-06-13T07:59:36.100616+00:00 app[web.1]: goroutine 727 [running]:
2019-06-13T07:59:36.100618+00:00 app[web.1]: net/http.(*conn).serve.func1(0xc00014c320)
2019-06-13T07:59:36.100621+00:00 app[web.1]: /app/tmp/cache/go1.12.5/go/src/net/http/server.go:1769 +0x139
2019-06-13T07:59:36.100623+00:00 app[web.1]: panic(0x6cf920, 0x9858a0)
2019-06-13T07:59:36.100624+00:00 app[web.1]: /app/tmp/cache/go1.12.5/go/src/runtime/panic.go:522 +0x1b5
2019-06-13T07:59:36.100627+00:00 app[web.1]: main.Message(0x78f4a0, 0xc000058d90, 0x792c40, 0xc0001500e0, 0xc0000b5a28, 0x40cdf9)
2019-06-13T07:59:36.100629+00:00 app[web.1]: /tmp/build_460942fe7080468b42a8e419284c6ff8/message.go:14 +0x65
2019-06-13T07:59:36.100631+00:00 app[web.1]: main.(*SlackService).PostEvent(0xc000058d90, 0x792c40, 0xc0001500e0, 0x3, 0x3, 0xc00001a270, 0x2c)
2019-06-13T07:59:36.100633+00:00 app[web.1]: /tmp/build_460942fe7080468b42a8e419284c6ff8/service.go:36 +0x98
2019-06-13T07:59:36.100636+00:00 app[web.1]: main.(*Server).Slack(0xc000010040, 0x792480, 0xc0000d2460, 0xc00006a200, 0xc00006c360, 0x3, 0x3)
2019-06-13T07:59:36.100638+00:00 app[web.1]: /tmp/build_460942fe7080468b42a8e419284c6ff8/server.go:118 +0x836
2019-06-13T07:59:36.100639+00:00 app[web.1]: github.com/julienschmidt/httprouter.(*Router).ServeHTTP(0xc000020480, 0x792480, 0xc0000d2460, 0xc00006a200)
2019-06-13T07:59:36.100641+00:00 app[web.1]: /app/tmp/cache/go-path/pkg/mod/github.com/julienschmidt/httprouter@v1.2.0/router.go:334 +0x948
2019-06-13T07:59:36.100643+00:00 app[web.1]: main.(*Server).ServeHTTP(0xc000010040, 0x792480, 0xc0000d2460, 0xc00006a200)
2019-06-13T07:59:36.100645+00:00 app[web.1]: /tmp/build_460942fe7080468b42a8e419284c6ff8/server.go:70 +0x4c
2019-06-13T07:59:36.100648+00:00 app[web.1]: net/http.serverHandler.ServeHTTP(0xc000092b60, 0x792480, 0xc0000d2460, 0xc00006a200)
2019-06-13T07:59:36.100650+00:00 app[web.1]: /app/tmp/cache/go1.12.5/go/src/net/http/server.go:2774 +0xa8
2019-06-13T07:59:36.100652+00:00 app[web.1]: net/http.(*conn).serve(0xc00014c320, 0x792a40, 0xc000180300)
2019-06-13T07:59:36.100653+00:00 app[web.1]: /app/tmp/cache/go1.12.5/go/src/net/http/server.go:1878 +0x851
2019-06-13T07:59:36.100655+00:00 app[web.1]: created by net/http.(*Server).Serve
2019-06-13T07:59:36.100657+00:00 app[web.1]: /app/tmp/cache/go1.12.5/go/src/net/http/server.go:2884 +0x2f4

Here's the relevant code:

https://github.com/dnsimple/strillone/blob/7471dc6e58bffe6ae597219d63345df4387edc03/message.go#L11-L14

Here's an example of a webhook that crashes:

{
  "data": {
    "account": {
      "id": 0,
      "email": "ops@example.com",
      "created_at": "2012-03-16T16:02:54Z",
      "updated_at": "2019-06-12T13:33:07Z",
      "plan_identifier": "monthly"
    },
    "account_invitation": {
      "id": 0,
      "email": "example@example.com",
      "token": "256bffc4",
      "account_id": 0,
      "created_at": "2019-06-13T07:45:29Z",
      "updated_at": "2019-06-13T07:45:29Z",
      "invitation_sent_at": "2019-06-13T07:45:29Z",
      "invitation_accepted_at": null
    }
  },
  "name": "account.user_invite",
  "actor": {
    "id": "0",
    "entity": "user",
    "pretty": "user@example.com"
  },
  "account": {
    "id": 0,
    "display": "Example",
    "identifier": "example"
  },
  "api_version": "v2",
  "request_identifier": "0e55bda3-8fdf-4ca2-8bcc-fce18417d40a"
}