BUG: MultiIndex.is_montonic erronoes when nan in at least one level

[phofl]

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• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

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Code Sample, a copy-pastable example

print(pd.MultiIndex.from_tuples([(np.nan, ), (1,)], names=["test"]).is_monotonic_increasing)

Problem description

This returns True, which is obviously not correct. This was introduced by #27495. The error persists with more than one level in the MultiIndex. The example is just for simplicity.

Expected Output

False

Output of pd.show_versions()

master