'Checks ``bundle.data``to ensure it is valid & replaces it with the
cleaned results.
If the form is valid, an empty list (all valid) will be returned. If
not, a list of errors will be returned.'

def is_valid(self, bundle, request=None):

    form = self.form_class(**self.form_args(bundle))
    if form.is_valid():
        bundle.data = form.cleaned_data
        return {}
    return form.errors
