#fixed code
                                protected void addChildren(int index, Node... children) {
        Validate.notNull(children);
        if (children.length == 0) {
            return;
        }
        final List<Node> nodes = ensureChildNodes();

        // fast path - if used as a wrap (index=0, children = child[0].parent.children - do inplace
        final Node firstParent = children[0].parent();
        if (firstParent != null && firstParent.childNodeSize() == children.length) {
            boolean sameList = true;
            final List<Node> firstParentNodes = firstParent.childNodes();
            // identity check contents to see if same
            int i = children.length;
            while (i-- > 0) {
                if (children[i] != firstParentNodes.get(i)) {
                    sameList = false;
                    break;
                }
            }
            firstParent.empty();
            nodes.addAll(index, Arrays.asList(children));
            i = children.length;
            while (i-- > 0) {
                children[i].parentNode = this;
            }
            reindexChildren(index);
            return;
        }

        Validate.noNullElements(children);
        for (Node child : children) {
            reparentChild(child);
        }
        nodes.addAll(index, Arrays.asList(children));
        reindexChildren(index);
    }
#vulnerable code 
                                protected void addChildren(int index, Node... children) {
        Validate.noNullElements(children);
        final List<Node> nodes = ensureChildNodes();

        for (Node child : children) {
            reparentChild(child);
        }
        nodes.addAll(index, Arrays.asList(children));
        reindexChildren(index);
    } 
                            #location 6 
                            #vulnerability type NULL_DEREFERENCE