Return default value for `stmt` node.

        `refd` is a dictionary of applicable refinements that is
        constructed in the `process_patches` method.

def get_default(self, stmt, refd):
        """Return default value for `stmt` node.

        `refd` is a dictionary of applicable refinements that is
        constructed in the `process_patches` method.
        """
        if refd["default"]:
                return refd["default"]
        defst = stmt.search_one("default")
        if defst:
            return defst.arg
        return None