The problem occurs when you want to use a very popular command line option: `--exports=xml`. (Side note: currently only `xml` is supported.) This option means "when the calculation finishes, export all of the results (as XML)". However, some formats, such as event loss tables and aggregate loss do not have an XML representation, yet we cannot just skip them. Furthermore, we can't exactly add the option to do `--exports=csv` until we have defined csv/text formats for all of the other artifacts.