MDR is not DFSG-compatible
Wolfgang was right about SPL not being free. MDR is a library that ArgoUML will use. ArgoUML is in contrib at the moment because of Swing issues so it can't be built and run with free software, but there are a lot of progresses in free Classpath based runtime. But now that ArgoUML will switch to MDR, we have another problem: SPL. It seems that SPL is not DFSG-compatible. Bad. I filed an issue on the Netbeans website (Issue#73161) to ask if they could change the license to one DFSG-compatible. If it's not possible, I'll have to package MDR to non-free and leave ArgoUML in contrib.