I'm developing a site and checking it with WP_DEBUG on.
When wp-pagenavi is active on the site I was getting getting debug notices like:
Notice: Undefined offset: in /home/sites/... .../wp-content/plugins/wp-pagenavi/core.php on line 17
line 17 of core.php is
$args[ $key ] = $argv[ $i ];
My fix was to change line 17 to
$args[ $key ] = isset( $argv[ $i ]) ? $argv[ $i ] : "";
After making that change, the notices no longer appear