Undefined index: error-codes in recaptcha_check_answer()

Overview

When non-authenticated user subscribes to mailing list at /civicrm/mailing/subscribe, checks the "I am not a robot" reCAPTCHA, and clicks subscribe. The subscription request is processed properly, but an error is thrown:

Notice: Undefined index: error-codes in recaptcha_check_answer() (line 159 of /bitnami/drupal/modules/contrib/civicrm/ext/recaptcha/lib/recaptcha/recaptchalib.php).

Reproduction steps

1. /civicrm/mailing/subscribe
2. complete email address, check relevant mailing list (in this case, "General Newsletter")
3. Check "I'm not a robot" in reCAPTCHA
4. Click "Subscribe"
5. Subscription is processed properly.
6. Error reported on confirmation page.

Current behaviour

Error message presented. Functionality of reCAPTCHA and subscription is okay.

Notice: Undefined index: error-codes in recaptcha_check_answer() (line 159 of /bitnami/drupal/modules/contrib/civicrm/ext/recaptcha/lib/recaptcha/recaptchalib.php).

Expected behaviour

No error message

Environment Information

• CiviCRM: 5.40.2
• PHP: 7.3.27
• CMS: Drupal 7.82
• Database: MySQL 5.7.33
• Web Server: Apache 2.4.46
• reCAPTCHA: Version 5.40.2