BUG: Series([pd.NA, np.nan], dtype="Float64").nunique() should return 0?

[mroeschke]

Pandas version checks

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Reproducible Example

In [22]: import pandas as pd; import numpy as np

In [23]: (pd.Series([np.nan, 0], dtype="Float64") / 0).nunique()
Out[23]: 1

Issue Description

The docs not that Excludes NA values by default.; therefore, should the result be 0?

Expected Behavior

Returns 0?

Installed Versions

Replace this line with the output of pd.show_versions()