Everytime I you want to create a  new articel exception is thrown

24.11.11 10:53: Exception Thrown
Context Path:/seappl/MarketingWiki.nsf
Page Name:/startPageNew.xsp
Script interpreter error, line=5, col=23: 'doc' is null
     3: var xview:NotesView=database.getView("vSysCat");
     4: var doc:NotesDocument=xview.getDocumentByKey(lookup,true);
->   5: var contentType = doc.getItemValueString("contentType");
     6: if(contentType == "prodDoc"){
     7:     requestScope.activeTab = "productDoc";

Thanks