home page periodical publishing

function mag_front_page_filter( $query ) {

if ( $query->is_home() && $query->is_main_query() ) {
if ( !get_query_var( 'issue' )){
$tax_query = array(
array(
'taxonomy' => 'issue' ,
'field' => 'slug',
'terms' => mag_get_current_issue(),
)
);
$query->set( 'tax_query' , $tax_query);
}
}
}

// register the filter
add_action( 'pre_get_posts', 'mag_front_page_filter' );