Type error on front events page when no events are returned [#3584954]

Problem/Motivation

The default /events page gives an TypeError: Drupal\Core\Form\OptGroup::flattenOptions(): Argument #1 ($array) must be of type array, false given, called in /var/www/html/web/core/lib/Drupal/Core/Form/FormValidator.php on line 351 in Drupal\Core\Form\OptGroup::flattenOptions() (line 23 of /var/www/html/web/core/lib/Drupal/Core/Form/OptGroup.php). when no events are included.

Steps to reproduce

Install intercept module onto Drupal 11 and access the front page and this error will be given.

Proposed resolution

It's a simply fix to return an empty array vs. False - this resolves the issue.

Remaining tasks

User interface changes

API changes

Data model changes

Issue fork intercept-3584954

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3584954-type-error-on changes, plain diff MR !24
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