code: private void updateInitSignature(int idx, State<O> succ) {
          StateSignature<O> sig = init.getSignature();
          State<O> oldSucc = sig.successors.array[idx];
          if (oldSucc == succ) {
              return;
          }
          if (oldSucc != null) {
              oldSucc.decreaseIncoming();
          }
          sig.successors.array[idx] = succ;
          succ.increaseIncoming();
      }
docs: Update the signature of the initial state. This requires special handling, as the initial state is not stored in
  the register (since it can never legally act as a predecessor).
  
  @param idx
  the transition index being changed
  @param succ
  the new successor state