This may not be exactly where to put it as I believe that this is a PFRPG ruleset issue not specific to the modules, but...
When rolling on an ability score of 0, the roll calculates the roll as a -5 as the modifier.
I would argue that the modifier for the roll should actually be 0.
Creatures generally are dead or in a coma with an ability score of 0 so the modifier doesn't really exist (there is no official modifier in the ability score table for a 0 score). However, creatures like constructs specifically say that they have no Constitution, yet their modifier for DCs should be 0.