fix(nx-plugin): add fallback for json.files property in preset

Author: brandonroberts

packages/nx-plugin/src/generators/init/lib/update-app-tsconfig.ts

@@ -25,10 +25,10 @@ export function updateAppTsConfig(
       tree,
       tsconfigPath,
       (json) => {
-        json.files = [...json.files, 'src/main.server.ts'];
+        json.files = [...(json.files || []), 'src/main.server.ts'];
 
         json.include = [
-          ...json.include,
+          ...(json.include || []),
           'src/app/pages/**/*.page.ts',
           'src/server/middleware/**/*.ts',
         ];