final public static function getInstance(?array $configurations = null): self
    {
        if (is_null(self::$instance)) {
            self::$instance = new self($configurations);
        }
        return self::$instance;
    }
final public static function getInstance(?array $configurations = null): self
    {
        if (is_null(self::$instance)) {
            self::$instance = new self($configurations);
        }
        return self::$instance;
    }
final public static function getInstance ( ? array $ configurations = null ) : self { if ( is_null ( self :: $ instance ) ) { self :: $ instance = new self ( $ configurations ) ; } return self :: $ instance ; }
Obtain the single allowed instance for Session through singleton pattern
method.

@return Session
Obtain the single allowed instance for Session through singleton pattern method .