fix(codegen): document.documentElement is null on early navigation (#33627)

packages/playwright-core/src/server/injected/highlight.ts

@@ -90,7 +90,8 @@ export class Highlight {
   }
 
   install() {
-    if (!this._injectedScript.document.documentElement.contains(this._glassPaneElement))
+    // NOTE: document.documentElement can be null: https://github.com/microsoft/TypeScript/issues/50078
+    if (this._injectedScript.document.documentElement && !this._injectedScript.document.documentElement.contains(this._glassPaneElement))
       this._injectedScript.document.documentElement.appendChild(this._glassPaneElement);
   }