tests contradicts each other

I would like to give some feedback about ...

From: https://py.checkio.org/mission/comp_funcs/solve/

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the third test, as below seems to require a None result being a valid result and let the output of f and g compare to each other.

    assert checkio(lambda n:("Fizz "*(1-n%3) + "Buzz "*(1-n%5))[:-1] or str(n),
               lambda n:('Fizz'*(n%3==0) + ' ' + 'Buzz'*(n%5==0)).strip())\
               (7)==('7','different'), "fizz buzz, third"

While at the same time, the below test seems to imply that a None result should be treated as an error.

f = lambda x: abs(x)
def g(x):
    if x>0:
        return x
    elif x<0:
        return -x
assert checkio(f,g)(0) == (0,'g_error')