[Jig] SESSION.csrf always return NULL

[Anand Pilania]

Recently I works with F3 (.6) Session and follows the instructions provided at: https://fatfreeframework.com/3.6/session

      $db = new DB\Jig ( $f3->get('DB_PATH'), DB\JIG::FORMAT_JSON );

      $session = new DB\Jig\Session ( $db, 'sessions', TRUE, NULL, 'CSRF' );

      $f3->copy ( 'CSRF', 'SESSION.CSRF' );

      var_dump ( [

        'f3->csrf' => $f3->CSRF,

        'Session->csrf()' => $session->csrf()

      ]);

So now, according to the official documentation, `$f3->CSRF` also holds the value of `csrf`, but its always return NULL and `$session->csrf()` holds the exact value of `csrf`... 

Is something wrong in my code??