Simplest quickstart example error- Invariant Violation: RenderForm.render()

Based on (a copy/paste, really) the example at the top of the [quickstart](http://newforms.readthedocs.org/en/latest/quickstart.html) I have the following:

```
var SignupForm = forms.Form.extend({
username: forms.CharField(),
email: forms.EmailField(),
password: forms.CharField({widget: forms.PasswordInput}),
confirmPassword: forms.CharField({widget: forms.PasswordInput}),
acceptTerms: forms.BooleanField({required: true})
});

var Signup = React.createClass({
render: function() {
return (


Sign Up

);
}
});
```

This fails with the following error in the chrome console:

```
Uncaught Error: Invariant Violation: RenderForm.render(): A valid ReactComponent must be returned. You may have returned undefined, an array or some other invalid object.
```

The problem seems to be in the `` line, if I remove that the error goes away, but of course I don't see my fields.