Comment 1 for bug 246724

This appears to be caused by the absence of an 'xlink:href' attribute on some 'image' element. The SVG specification requires the 'xlink:href' attribute, but I doubt that Inkscape enforces this (on 'image' elements that it didn't create itself), so the script ought to deal gracefully with the absence (e.g, by just ignoring 'image' elements that have no 'xlink:href' attribute).