Changeset 6229 breaks the atom feed

[rubys]

Once ​6229 is applied, the following is seen in the Atom feed:

<br />
<b>Warning</b>:  Invalid argument supplied for foreach() in 
<b>/home/rubys/svn/wordpress/wp-includes/feed.php</b> on line <b>243</b><br />

[rubys]

Example output: ​http://intertwingly.net/stories/2007/10/ape/validate.html

[ryan]

(In [6247]) Allow single post ID and comma delimited list of post IDs to be passed to update_postmeta_cache(). Fix default cache to allow storage of empty array. see #5194

[ryan]

Try that on.