Deprecated function: parse_str(): Passing null to parameter #1 ($string) of type string is deprecated

Problem/Motivation

The following PHP error is occurring when sending mail with Mime Mail:

Deprecated function: parse_str(): Passing null to parameter #1 ($string) of type string is deprecated in Drupal\mimemail\Utility\MimeMailFormatHelper::mimeMailUrl() (line 598 of modules/contrib/mimemail/src/Utility/MimeMailFormatHelper.php).
Drupal\mimemail\Utility\MimeMailFormatHelper::mimeMailUrl() (Line: 211)
Drupal\mimemail\Utility\MimeMailFormatHelper::Drupal\mimemail\Utility\{closure}()
preg_replace_callback() (Line: 203)
Drupal\mimemail\Utility\MimeMailFormatHelper::mimeMailHtmlBody() (Line: 214)
Drupal\mimemail\Plugin\Mail\MimeMail->prepareMessage() (Line: 107)
Drupal\mimemail\Plugin\Mail\MimeMail->format() (Line: 43)
Drupal\mailsystem\Adapter->format() (Line: 291)
Drupal\Core\Mail\MailManager->doMail() (Line: 181)
Drupal\Core\Mail\MailManager->Drupal\Core\Mail\{closure}() (Line: 627)
Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 180)
Drupal\Core\Mail\MailManager->mail() (Line: 70)
Drupal\mailsystem\MailsystemManager->mail() (Line: 597)

Steps to reproduce

Drupal 11.2.5
PHP 8.3.14
Mimemail 2.0.0

We have a custom module that sends email notifications to reviewers when content nodes are updated. So try this recipe to reproduce:

1. Go to Configuration->System->Mail System and set the Formatter to "Mime Mail mailer".
2. Create a custom module that implements hook_entity_update()
3. In the hook_entity_update() function, send an email by calling \Drupal::service('plugin.manager.mail')->mail('employees', $key, $to, $langcode, $params, $from, true); (using appropriate values for those variables)
4. Edit and save a content node to trigger the hook_entity_update and send an email. The error is shown at the top of the next page.

I used xdebug to inspect MimeMailFormatHelper.php. On line 571, $url = "/node/25399/revisions/98313/view", which causes $query = null on line 573 and 598.

Proposed resolution

Change line 598 to

parse_str($query ?? "", $arr);

Remaining tasks

User interface changes

API changes

Data model changes