[Airbrake] [Swarm] Cannot read property 'push' of undefined

[citizencodebot]

Check full details on Airbrake: #1625188559780173168

Airbrake project: swarmbot-staging

Backtrace:

/app/node_modules/slack-client/src/channel.js:73:in Channel.addMessage
/app/node_modules/slack-client/src/client.js:482:in Client.onMessage
/app/node_modules/slack-client/src/client.js:140:in 
events.js:87:in emitTwo
events.js:172:in WebSocket.emit
/app/node_modules/slack-client/node_modules/ws/lib/WebSocket.js:697:in Receiver.self._receiver.ontext
/app/node_modules/slack-client/node_modules/ws/lib/Receiver.js:397:in Receiver.opcodes.1.finish
/app/node_modules/slack-client/node_modules/ws/lib/Receiver.js:384:in Receiver.expectHandler
/app/node_modules/slack-client/node_modules/ws/lib/Receiver.js:93:in Receiver.add
/app/node_modules/slack-client/node_modules/ws/lib/WebSocket.js:678:in TLSSocket.firstHandler
events.js:77:in emitOne
events.js:169:in TLSSocket.emit
_stream_readable.js:146:in readableAddChunk
_stream_readable.js:110:in TLSSocket.Readable.push
net.js:523:in TLSWrap.onread