cannot get distortion coefficient for pfi_sky transform.

In [1]: import pfs.utils.coordinates.DistortionCoefficients as DCoeff

In [2]: c = DCoeff.Coeff('pfi_sky')
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KeyError                                  Traceback (most recent call last)
Input In [2], in <cell line: 1>()
----> 1 c = DCoeff.Coeff('pfi_sky')

File ~/devel/drp/pfs_utils/python/pfs/utils/coordinates/DistortionCoefficients.py:375, in Coeff.__init__(self, mode)
    373 self.skip1_off = skip1_off[mode]
    374 self.skip2_off = skip2_off[mode]
--> 375 self.do_off2 = do_off2[mode]
    376 self.slp = dic_slp[mode]
    377 self.dsc = dic_dsc[mode]

KeyError: 'pfi_sky'