def _(): assert bf.mode([1, 2, 3, 4, 5, 1]) == 1
def _(): assert bf.mode([1, 2, 3, 4, 5, 6]) == None
def _(): assert bf.mode([1, 1]) == 1
def _(): assert bf.mode([1, 2]) == None
def _(): assert bf.mode([]) == None