Query for user reference field Drupal 8

Query for user reference field Drupal 8

    $query = \Drupal::database()->select('node', 'n');
    $query->fields('n', ['nid','type']);
	$query->condition('type', array('basic'), 'IN');		// Basic is content type
	$query->leftJoin('node__field_user_ref', 'UID', "n.nid = UID.entity_id");	// field_user_ref is entity field for user reference 
	$query->condition('UID.field_user_ref_target_id', NULL, 'IS NOT NULL');
    $pager = $query->extend('Drupal\Core\Database\Query\PagerSelectExtender')->limit(50);
    $results = $pager->execute()->fetchAll();