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Hi,
A workaround:
@startumlclass "Header" as hclass bbbh <|- bbb@enduml
http://www.plantuml.com/plantuml/uml/SoWkIImgAStDuKhEIImkLb3oI4rCIIrIKaWiLiY0YYKb9N5bADZKw89P3gbvAK3r0000