The issue with the servant lady sounds more like an oversight, but I can take a look at it.
And congrats on getting that much def. :D NULL sounds like the game is trying to tell you it's 0. When an enemy attacks your character, the character's def gets subtracted from the total damage. 100 def would negate the damage completely from lower level enemies. I need to check to what extent this applies to upper level enemies, but enjoy being unkillable for now~