final Node<K, V> nextNode() {
      Node<K, V> e = next;
      if (e == header) {
        throw new NoSuchElementException();
      }
      if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
      }
      next = e.next;
      return lastReturned = e;
    }
This stack is a singly linked list, linked by the 'parent' field.
lottie/src/main/java/com/airbnb/lottie/parser/moshi/LinkedHashTreeMap.java