After upgrading to 3.0 it is not possible to use already created sessions

The issue is mute_on_start(). On migration a new column `
muteonstart` is added to the database, and it default value is set to false. But on existing instances, the value given is null (perhaps not all databases, but it has not been confirmed).

it is necessary to add a validation  statement in the instance.php file, function get_mute_on_start() to be able to access the recordings again.

One solution is:

public function get_mute_on_start(): bool {

  if ($this->get_instance_var('muteonstart') === null) return 0; else return $this->get_intance_var('muteonstart');

}

Another one is:

publicfunctionget_mute_on_start(): bool {

  returnboolval($this->get_instance_var('muteonstart'));

} 

To reproduce:
-Edit the value in the database on any instance. Set to null (to emulate the value after migration)