Fatal PHP error in setContext if subscriber was deleted

$current_subscriber = User::load($this->uid);
if (is_object($current_subscriber)) {
  \Drupal::service('account_switcher')->switchTo($current_subscriber);
}

Could this be simplified to:

if ($current_subscriber = User::load($this->uid)) {
  \Drupal::service('account_switcher')->switchTo($current_subscriber);
}

?

That's basically what you did for the other hunk:

-    if ($this->uid) {
+    if ($this->uid && User::load($this->uid)) {

I think in the feature will be better to implement the functionality -> then a user is deleting from a site, unsubscribe a user from each newsletter.

Simplenews subscribers can be anonymous users, so I'm not sure this should be the automatic behavior. It's very easy to implement using hooks if a site wants to do that, probably not necessary to force it to be that way. It'd be harder to allow sites to prevent it than it is to allow sites to do it themselves.

Great! Sorry Ruslan, I forgot to say: the maintainers are probably going to want a test for this before they commit it.

Confirm that normal policy for this module is that tests are needed - in the long run it's the best way to get a stable module.

There can be exceptions for example if you are fixing a small bug in a certain feature, and there are no existing tests to adapt.

In simplenews_user_delete() there is code to delete the subscriber so maybe this is now fixed?