`clear` not defined?

I can't seem to use `clear` on my database.

```coffeescript
nStore = require 'nstore'
nStore.new 'data/pets.db', (err, petsDB) ->
  return console.log err if err?
  petsDB.clear (err) ->
    console.log err if err?
```

I get an error:

> TypeError: Object #<Object> has no method 'clear'

Am I doing something wrong?