facebook/immutable-js — pull request #250 by Dashed (2014-12-17 16:35:02+00:00)
Title: Be able to set value of a cursor

Add:
```js
Cursor.set(value: any): Cursor
```

Similar to `update(updater: (value: any) => any): Cursor`, but with being able to set `undefined`.

Closes https://github.com/facebook/immutable-js/issues/249