overlapped groups in nwdiag throws exception

Question

@startuml

nwdiag {

internet [ shape = cloud];

internet -- router;

group {

color = "pink";

app;

db;

}

group {

color = "blue"

router;

db;

}

network proxy {

router;

app;

}

network default {

app;

db;

}

}

@enduml