Guard against real-time messaging API returning empty users

[technicalpickles]

I've been having problems with hubot crashing periodically, usually overnight when no one is activel. I found errors in the log like:

TypeError: Cannot read property 'email' of undefined
  at SlackBot.userChange (node_modules/hubot-slack/src/slack.coffee:79:7, <js>:113:36)
  at SlackBot.__bind [as userChange] (node_modules/hubot-slack/src/slack.coffee:1:1, <js>:3:61)
  at SlackBot.loggedIn (node_modules/hubot-slack/src/slack.coffee:64:7, <js>:83:28)
  at Client.__bind (node_modules/hubot-slack/src/slack.coffee:1:1, <js>:3:61)
  at Client.EventEmitter.emit (events.js:96:17)
  at Client._onLogin (node_modules/hubot-slack/node_modules/slack-client/src/client.js:100:14)
  at __bind (node_modules/hubot-slack/node_modules/slack-client/src/client.js:2:59)
  at IncomingMessage.Client._apiCall.req.on.callback.ok (node_modules/hubot-slack/node_modules/slack-client/src/client.js:670:22)

The line the error is coming from user.profile.email, which indicates the user.profile is undefined, so I first tried an existential operator, ie user.profile?.email. Crashes still happened, but with a different error:

[Thu Sep 24 2015 05:31:55 GMT-0700 (PDT)] ERROR TypeError: Cannot call method 'toString' of undefined
  at new User (/data/hubot/node_modules/hubot/src/user.coffee:9:19, <js>:14:47)
  at Brain.userForId (/data/hubot/node_modules/hubot/src/brain.coffee:106:7, <js>:93:16)
  at SlackBot.userChange (/data/hubot/node_modules/hubot-slack/src/slack.coffee:94:5, <js>:134:31)
  at SlackBot.__bind [as userChange] (/data/hubot/node_modules/hubot-slack/src/slack.coffee:1:1, <js>:3:61)
  at SlackBot.loggedIn (/data/hubot/node_modules/hubot-slack/src/slack.coffee:64:7, <js>:83:28)
  at Client.__bind (/data/hubot/node_modules/hubot-slack/src/slack.coffee:1:1, <js>:3:61)
  at Client.EventEmitter.emit (events.js:96:17)
  at Client._onLogin (/data/hubot/node_modules/hubot-slack/node_modules/slack-client/src/client.js:100:14)
  at __bind (/data/hubot/node_modules/hubot-slack/node_modules/slack-client/src/client.js:2:59)
  at IncomingMessage.Client._apiCall.req.on.callback.ok (/data/hubot/node_modules/hubot-slack/node_modules/slack-client/src/client.js:670:22)
  at IncomingMessage.EventEmitter.emit (events.js:123:20)
  at IncomingMessage._emitEnd (http.js:366:10)
  at HTTPParser.parserOnMessageComplete [as onMessageComplete] (http.js:149:23)
  at CleartextStream.socketOnData [as ondata] (http.js:1366:20)
  at CleartextStream.CryptoStream._push (tls.js:526:27)
  at SecurePair.cycle (tls.js:880:20)
  at EncryptedStream.CryptoStream.write (tls.js:267:13)
  at Socket.ondata (stream.js:38:26)
  at Socket.EventEmitter.emit (events.js:93:17)
  at TCP.onread (net.js:396:14)

I added some debug logging to see what user was coming in, and it was empty, ie {} rather than a full profile. This is coming directly from the real-time messaging API so I've reported this issue to Slack, but in the mean time checking for user?.id? should be sufficient to guard against it.