docs: public void nextNull() throws IOException {
      int p = peeked;
      if (p == PEEKED_NONE) {
        p = doPeek();
      }
      if (p == PEEKED_NULL) {
        peeked = PEEKED_NONE;
        pathIndices[stackSize - 1]++;
      } else {
        throw new IllegalStateException("Expected null but was " + peek() + locationString());
      }
    }