Hm.. how about `throw "Item was no journal article";` ? 

But in this way the multiple picking is not working at all if you also select a non-article (e.g. all select all), while at the moment it works for all selected article. For example here http://www.digizeitschriften.de/dms/toc/?PPN=GDZPPN002612089 the multiple picking will only work when you select only (real) journal articles. I can go with both solutions...