Fix linters

Author: martinRenou

.eslintrc.js

@@ -37,6 +37,7 @@ module.exports = {
     '@typescript-eslint/no-explicit-any': 'off',
     '@typescript-eslint/no-namespace': 'off',
     '@typescript-eslint/no-var-requires': 'off',
+    '@typescript-eslint/explicit-module-boundary-types': 'off',
     '@typescript-eslint/no-use-before-define': 'off',
     '@typescript-eslint/no-empty-interface': 'off',
     '@typescript-eslint/quotes': [

packages/jupyterlab-preview/src/preview.tsx

@@ -150,8 +150,8 @@ export class VoilaPreview extends DocumentWidget<IFrame, INotebookModel> {
    * Reload the preview.
    */
   reload(): void {
-    const iframe = this.content.node.querySelector('iframe')!;
-    if (iframe.contentWindow) {
+    const iframe = this.content.node.querySelector('iframe');
+    if (iframe && iframe.contentWindow) {
       iframe.contentWindow.location.reload();
     }
   }