code: public function fetchAll($columns = null, \Closure $Closure = null)
      {
          $select = $this->getSelect();
          if ($columns) {
              $select->columns($columns);
          }
          if ($Closure) {
              $Closure($select);
          }
          return $this->select($select);
      }
docs: gets users list
  
  @param array                                     $columns columns to fetch from user table
  @param callable|\PrivateMessaging\Mapper\Closure $Closure $Closure       to manipulate Select
  
  @return \Zend\Db\ResultSet\ResultSet