add test case for `null` of (picrin control for)
add test case for `null` of (picrin control for)

ktakashi/picrin,omasanori/picrin,picrin-scheme/picrin,dcurrie/picrin,leavesbnw/picrin,ktakashi/picrin,leavesbnw/picrin,koba-e964/picrin,leavesbnw/picrin,picrin-scheme/picrin,omasanori/picrin,koba-e964/picrin,koba-e964/picrin,ktakashi/picrin,dcurrie/picrin