Debug notice when converting 2.0.23 to 3.0.2

Hello,

I have debug mode enabled and converted my 2.0.23 database to Olympus again. At the end of the conversion it tells "Conversion ready" [Konvertierung abgeschlossen] and at this point I can see the following message in the footer:

[phpBB Debug] PHP Notice: in file /includes/functions.php on line 4026: Undefined index: gzip_compress

These are the lines 4025 and 4026:

	// As a pre-caution... some setups display a blank page if the flush() is not there.

	(!$config['gzip_compress']) ? @flush() : @ob_flush();

Regards
Wolfgang