add on_missing keyword to mne.chpi.get_active_hpi() (#11163)
add on_missing keyword to mne.chpi.get_active_hpi() (#11163)

Co-authored-by: Eric Larson <14e6e0d1a6421c3f4a71ec06bfae870e115e40b0@gmail.com>
Teekuningas/mne-python,drammock/mne-python,wmvanvliet/mne-python,Teekuningas/mne-python,wmvanvliet/mne-python,wmvanvliet/mne-python,mne-tools/mne-python,mne-tools/mne-python,drammock/mne-python,Teekuningas/mne-python,mne-tools/mne-python,drammock/mne-python