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definition of constructor from CategoryViewer.php:

	function __construct( $title, IContextSource $context, $from = '', $until = '', $query = array() ) {
[...]
}

but later in function doCategoryQuery:
[...]
			if ( $this->from[$type] !== null ) {
[...]
and in private function getSectionPagingLinks( $type ):
[...]
		} elseif ( $this->nextPage[$type] !== null || $this->from[$type] !== null ) {
[...]

Parameter "from" should be probably defined in constructor as empty array() and/or later in code added to some is_array() condition.