Latest commit 920e72e Jan 9, 2017 @slorber slorber committed with timdorr Update combineReducers.js (#2187)
This may not seem obvious to many of us, but we can write

```
const bootstrapDataReducer = (state = null, event) => {
  switch (event.name) {
    case APPLICATION_STARTED:
      return event.data.bootstrapData;
    default:
      return state;
  }
};
```
instead of 

```
const bootstrapDataReducer = (state = {}, event) => {
  switch (event.name) {
    case APPLICATION_STARTED:
      return event.data.bootstrapData;
    default:
      return state;
  }
};
```

Assigning an empty object as initial state looks to me an anti-pattern, yet many people tend to do this to satisfy Redux

I think it would give a better developer experience to document the ability to use "null" instead of "undefined" as reducer state in error messages