The null middleware will be initialized to a default array of middlewares on line 88 of the same file.

```js
middleware = createDefaultMiddleware.call(this, connect, options);
```

My intent in the docs is to document that the default array of middlewares will be used when the value of `options.middleware` is `null` or `undefined`.  The subsequent lines in the documentation that you reference provide simple examples of passing a non-null value, either as an Array or as a function.

Does this work for you?