Save self form.

async def save_form(self, form, request, **resources):
        """Save self form."""
        if not self.can_create and not self.resource:
            raise muffin.HTTPForbidden()

        if not self.can_edit and self.resource:
            raise muffin.HTTPForbidden()

        resource = self.resource or self.populate()
        form.populate_obj(resource)
        return resource