Thread:Project:Support desk/Special:Upload - Argument 2 is not an array

I've just upgraded by Mediawiki from v1.6.1 to v1.23.5, running under PHP v5.4.25. MW runs in my root directory. On visiting the Special:Upload page, I originally saw a blank screen, but on enabling error reporting, I see the following error message:

Warning: array_diff: Argument #2 is not an array in /path/root-direct/includes/Setup.php on line 362 Warning: array_values expects parameter 1 to be array, null given in /path/root-direct/includes/Setup.php on line 362 Warning: array_unique expects parameter 1 to be array, null given in /path/root-direct/includes/specials/SpecialUpload.php on line 919 Catchable fatal error: Argument 1 passed to Language::commaList must be of the type array, null given, called in .. /path/root-direct/includes/specials/SpecialUpload.php on line 919 and defined in /path/root-direct/languages/Language.php on line 3266
 * Now that I have errors enabled, I see that the first two warnings (to Setup.php on line 362) appear on every page, so I guess that the Catchable fatal error is causing the problems with Special:Upload

In my LocalSettings.php file, I do not have either $wgFileExtensions, nor $wgFileBlacklist, defined.

includes/Setup.php on line 362 $wgFileExtensions = array_values( array_diff ( $wgFileExtensions, $wgFileBlacklist ) );

/specials/SpecialUpload.php on line 919 $this->getContext->getLanguage->commaList( array_unique( $wgFileExtensions ) )

languages/Language.php on line 3266+ function commaList( array $list ) { return implode(		wfMessage( 'comma-separator' )->inLanguage( $this )->escaped,		$list	); }