Illegal offset type in Drupal\mailjet\Form\DomainSettingsForm->buildForm() . Trusted domains tab has no effect

Error in logs:
Warning: Illegal offset type in Drupal\mailjet\Form\DomainSettingsForm->buildForm() (line 55 of /mysite/html/modules/contrib/mailjet/src/Form/DomainSettingsForm.php)

Here is the code that seems to be causing an issue:

    if ($domains = mailjet_user_domain_list()) {
      foreach ($domains as $domain) {
        if (!is_string($domain['Email'])) {
          $email = $domain['Email']['Email'];
        }
        else {
          $email = $domain['Email'];
        }
        $options[$email] = [
          'domain' => str_replace('*@', '', $email),
          'enabled' => $domain['Status'],
          'file_name' => $domain['Filename'],
        ];
      }
    }

Most likely the $email variable doesn't have any value.