via Erik Thauvin:

There's a bug in the Blojsom CommentAPI Servlet... I was looking at the
source to implement my own, and noticed that if an element is empty, it
throws a NPE.

http://cvs.sourceforge.net/viewcvs.py/blojsom/blojsom-2.0/extensions/src/org/blojsom/extension/comment/CommentAPIServlet.java?rev=1.16&view=markup

For example:

curl --header "Content-type: text/xml" --data
"<item><title>Test</title><author>erik@thauvin.net</author><description>Posted
via cURL.</description><link></link></item>"
"http://www.blojsom.com/commentapi/david/of+the+day/quote/?permalink=Tomorrow-Silverchair.html"

The <link/> element is empty, which is perfectly legal.

The problem is with the node.getFirstChild().getNodeValue() calls which
don't seem to like empty elements.