debug error on line 233

You have a line that causes a debug error (undefined index: cb) on line 233 whenever I edit an individual category:

$new_columns['cb'] = $columns['cb'];

I am not sure why you are setting this since you unset it 2 lines later:

function z_taxonomy_columns( $columns ) {
    $new_columns = array();
    $new_columns['cb'] = $columns['cb'];
    $new_columns['thumb'] = __('Image', 'categories-images');

    unset( $columns['cb'] );

    return array_merge( $new_columns, $columns );
}

Other things that may be useful to know: This is a custom taxonomy

Thanks