TypeError: Cannot read property 'start' of undefined

```
TypeError: Cannot read property 'start' of undefined
  File "/app/node_modules/gameanalytics-node-sdk/src/index.js", line 147, in _request.then
              start: this.users[user].start,
  File "internal/process/next_tick.js", line 68, in process._tickCallback
```

This happens to me sometimes, and I'm not sure why. It looks like there is no `catch` on sessionStart.