File::getErrorMessage

public function getErrorMessage()
{
	$m = [];
	for ($this->errorCollection->rewind(); $this->errorCollection->valid(); $this->errorCollection->next())
	{
		/** @var Error $error */
		$error = $this->errorCollection->current();
		$m[] = ($error->getMessage()?:$error->getCode());
	}
	return implode("", $m);
}