Prefer nothing over empty templates (#15633)

src/dialogs/voice-command-dialog/ha-voice-command-dialog.ts

@@ -12,7 +12,7 @@ import {
   html,
   LitElement,
   PropertyValues,
-  TemplateResult,
+  nothing,
 } from "lit";
 import { customElement, property, query, state } from "lit/decorators";
 import { classMap } from "lit/directives/class-map";
@@ -86,9 +86,9 @@ export class HaVoiceCommandDialog extends LitElement {
     fireEvent(this, "dialog-closed", { dialog: this.localName });
   }
 
-  protected render(): TemplateResult {
+  protected render() {
     if (!this._opened) {
-      return html``;
+      return nothing;
     }
     return html`
       <ha-dialog