如何列出特定自定义字段为空的帖子？

我有一些带有自定义字段“author”的帖子，有些帖子的自定义字段是emty，所以我想找到这些帖子来删除自定义字段。

<?php 
$args=array(
\'post_type\' => \'post\', // Post type is post.
\'post_status\' => \'publish\', // Post is published.
\'meta_key\' => \'author\',
\'value\'   => \'\',
\'meta_compare\' => \'=\',

\'posts_per_page\' => 100, // Posts per page.
\'caller_get_posts\'=> 100 // Get posts per page
);
$my_query = null;
$my_query = new WP_Query($args);
if( $my_query->have_posts() ) {
while ($my_query->have_posts()) : $my_query->the_post(); ?>

<?php // my code; ?>

<?php
endwhile;
}
?>