code: public function setStatementClass($statementClass)
      {
          if (!is_callable($statementClass) && !class_exists($statementClass)) {
              throw new \InvalidArgumentException('$statementClass must be a valid classname or a PHP callable');
          }
  
          $this->statementClass = $statementClass;
          return $this;
      }
docs: Set the classname of the statement class or callable that returns an object that
  implements the StatementInterface.
  
  The callable is passed the account object and statement sequence number
  as parameters. Example:
  
  $reader->setStatementClass(function (AccountInterface $account, $number) {
  return new My\Statement();
  });
  
  If the callable returns null, the statement is skipped.
  
  @param string|callable $statementClass
  @return $this