I think you would need to implode(‘,’,$excluded_pages) for things to work,
$excluded_pages = array();
$all_pages = get_pages();
foreach ( $all_pages as $the_page ) {
if ( '' == $the_page->post_content ) {
$excluded_pages[] = $the_page->ID;
}
}
wp_list_pages( array(
'exclude' => implode(',',$excluded_pages)
) );
EDIT