Lines 320 to 325 of numpy/polynomial/_polybase.py contains the following code:

        # filter out uninteresting coefficients
        filtered_coeffs = [
            (i, c)
            for i, c in enumerate(self.coef)
            # if not (c == 0)  # handle NaN
        ]

A few things to note:

1. the comment no longer describes what the comprehension does
2. the conditional is commented out
3. resulting list is never used

Looks like this is just some leftover code from a prior implementation that has caused no problems, as so has been overlooked.