Add Deliveries

Elwig/Documents/Document.cshtml.cs

@@ -43,8 +43,10 @@ namespace Elwig.Documents {
             string name;
             if (this is BusinessLetter) {
                 name = "BusinessLetter";
+            } else if (this is DeliveryNote) {
+                name = "DeliveryNote";
             } else {
-                throw new InvalidOperationException();
+                throw new InvalidOperationException("Invalid document object");
             }
             return await Html.CompileRenderAsync(name, this);
         }