If you update a record with no attributes, you'll hit a 500 from a guard
in `assign_attributes` raising:

```ruby
ArgumentError: When assigning attributes, you must pass a hash as an argument.
    app/controllers/users_controller.rb:44:in `block in update'
    app/controllers/users_controller.rb:43:in `update'
    test/controllers/users_controller_test.rb:37:in `block in <class:UsersControllerTest>'
```

Not a biggie, but may be quite confusing for the folks new to the
framework.