Docbook5-xsl-1.72.0 gives the following error message on <link> elements that have an xlink:href attribute but no content:
Link element has no content and no Endterm. Nothing to show in the link to http://example.org
This did work properly with 1.71.0, and it's allowed according to the DocBook Guide (http://www.docbook.org/tdg5/en/html/link.html):
"When the content of the link element is empty, the content of the xlink:href attribute should be rendered as the text of the link."
Visit <link xlink:href="http://example.org" />.
A quick patch that fixed the problem for me is attached. (However, looking at the DocBook 1.71.0 sources, this patch may not be sufficient; 1.71.0 seems to treat links starting with '#' specially.)