Should probably first check that the given datastream exists on the object, before trying to create a URL to something that potentially doesn't exist...  Or at least make it so we don't add the 'enclosure' to the 'items' bit below, when the object doesn't contain the datastream...  Though on second though, we don't have the object instantiated at this point...  Are a bunch of potential 404s gonna be a problem? Not really sure how/if the enclosure stuff gets used.