Update views.py for public superevent page:

For S191216ap, the p_terrestrial value was so small:
pastro_values=[('BNS', 0.0), ('NSBH', 0.0), ('BBH', 0.0), ('Terrestrial', 8.427577149405988e-16), ('MassGap', 0.9999999999999991)]

python was converting it to a NoneType, which would then fail when you tried to sort or compare values. So, for this view, convert NoneType probabilities to 0.0.