fix(a11y-core): give ad-hoc virtual nodes a null parent

lib/commons/aria/get-owned-virtual.js

@@ -15,9 +15,12 @@ function getOwnedVirtual(virtualNode) {
   // TODO: Descend into children with role=presentation|none
   // TODO: Exclude descendents owned by other elements
   if (virtualNode.hasAttr('aria-owns')) {
+    // [a11y-critical]: getNodeFromTree returns undefined for a ref outside the
+    // current tree, so the resolved nodes need filtering too, not just the refs
     const owns = idrefs(actualNode, 'aria-owns')
       .filter(element => !!element)
-      .map(element => axe.utils.getNodeFromTree(element));
+      .map(element => axe.utils.getNodeFromTree(element))
+      .filter(vNode => !!vNode);
 
     // Deduplicates by first occurrence to match browser accessibility tree behavior
     // See: https://github.com/dequelabs/axe-core/pull/4987

lib/commons/dom/create-grid.js

@@ -41,7 +41,9 @@ export default function createGrid(
   if (!parentVNode) {
     let vNode = getNodeFromTree(document.documentElement);
     if (!vNode) {
-      vNode = new VirtualNode(document.documentElement);
+      // [a11y-critical]: null marks the top of the tree; undefined means
+      // "disconnected" and makes any closest() walk through this node throw
+      vNode = new VirtualNode(document.documentElement, null);
     }
 
     nodeIndex = 0;

lib/core/utils/dq-element.js

@@ -50,7 +50,9 @@ export function truncateElement(element) {
 
   let vNode = getNodeFromTree(element);
   if (!vNode) {
-    vNode = new VirtualNode(element);
+    // [a11y-critical]: null marks the top of the tree; undefined means
+    // "disconnected" and makes any closest() walk through this node throw
+    vNode = new VirtualNode(element, null);
   }
   const { nodeName } = vNode.props;