fix(app-check): guard missing initializeAppCheck options at runtime

reject undefined options with same error as other path before native initialization.

Author: mikehardy

packages/app-check/__tests__/appcheck.test.ts

@@ -20,6 +20,12 @@ describe('appCheck()', function () {
       expect(initializeAppCheck).toBeDefined();
     });
 
+    it('`initializeAppCheck` rejects missing options at runtime', async function () {
+      await expect(initializeAppCheck(undefined, undefined)).rejects.toThrow(
+        'Invalid configuration: no options defined.',
+      );
+    });
+
     it('`getToken` function is properly exposed to end user', function () {
       expect(getToken).toBeDefined();
     });

packages/app-check/lib/index.ts

@@ -18,8 +18,8 @@
 import {
   isBoolean,
   isIOS,
-  isString,
   isObject,
+  isString,
   isUndefined,
   isOther,
   parseListenerOrObserver,
@@ -258,8 +258,11 @@ export async function initializeAppCheck(
   app?: FirebaseApp,
   options?: AppCheckOptions,
 ): Promise<AppCheck> {
+  if (!isObject(options)) {
+    throw new Error('Invalid configuration: no options defined.');
+  }
   const appCheck = getModularAppCheck(app);
-  await (appCheck as AppCheckInternal).initializeAppCheck(options as AppCheckOptions);
+  await (appCheck as AppCheckInternal).initializeAppCheck(options);
   return appCheck;
 }