Remove internal fields

def clean(self, user=None):
        """Remove internal fields"""
        doc = self._resource
        internal_fields = deepcopy(self.internal_fields)
        if user is None or not user.is_user(self.organisation_id):
            internal_fields.append('permissions')

        result = {k: v for k, v in doc.iteritems() if k not in internal_fields}

        return result