Illustrate how to check the value of ```post__in``` before it is used to construct a new ```WP_Query``` object.

example.php

<?php
$my_posts = false;

$my_post_ids = mytheme_get_special_post_ids();

if ( ! empty( $my_post_ids ) ) {
	$my_posts = new WP_Query( array(
		'post__in'       => $my_post_ids,
		'post_status'    => 'publish',
		'posts_per_page' => 10,
		'no_found_rows'  => true,
	) );
}

if ( $my_posts ) {
	// Do something with the posts here.
}