Got crash when remove person


hi, I got a crash when remove a person:
here is the call stack(No exception raised, it’s a EXC_BAD_ACCESS fault):


emm… as what i guessed, it’s a invalid pointer fault, so i deleted the remove button’s second method-“canRemove”, it’s worked. And i clicked Remove button when table is empty, no crash happened, so that’s the solution, i guess.