actually I thought of a problem with this. if any of these values is 0 it will default to null.

so, needs to be `latitude = (typeof req.body.latitude === 'undefined') ? null : req.body.latitude`

which is ugly.

what about this:
```
var opts = _.defaults(_.clone(req.body), {
  latitude: null
  , longitude: null
  , ...
});

if (checkMissingParams(res, {latitude: opts.latitude, longitude: opts.longitude})) {
  req.device.setLocation(opts.latitude, opts.longitude, ...);
}
```

still keeps you from having another definition block but avoids the javascript fuzzy equals problem.