fix(cdk/a11y): add parent node check to AriaDescriber (#19951)

Adds a check for `parentNode` when removing a description node in AriaDescriber.

Fixes #19949

Author: HELiving

src/cdk/a11y/aria-describer/aria-describer.ts

@@ -167,8 +167,8 @@ export class AriaDescriber implements OnDestroy {
       // already a container on the page, but we don't have a reference to it. Clear the
       // old container so we don't get duplicates. Doing this, instead of emptying the previous
       // container, should be slightly faster.
-      if (preExistingContainer) {
-        preExistingContainer.parentNode!.removeChild(preExistingContainer);
+      if (preExistingContainer && preExistingContainer.parentNode) {
+        preExistingContainer.parentNode.removeChild(preExistingContainer);
       }
 
       messagesContainer = this._document.createElement('div');