When there is an error, second argument passed to callback is the error too

Is this on purpose?

``` javascript
db.get('foo', 'bar', function(err, bar) {
  console.log(arguments);
}
```

results in

``` javascript
{ '0': { [Error: not found] message: 'not found', statusCode: 404, notFound: true },
  '1': { [Error: not found] message: 'not found', statusCode: 404, notFound: true },
```
