Hi,
When I start the activity diagram with a split and hide all the arrows entering it, the horizontal line is still shown.
@startumlsplit -[hidden]-> :A;split again -[hidden]-> :B;split again -[hidden]-> :C;end split:D;@enduml
http://www.plantuml.com/plantuml/png/SoWkIImgAStDuIekoCaiuL9GKD2DpiXCIKdDYzMr0t6j7AqXSWg9wOcPUTXKE15KuMpDbPgNeW2nmyh5cii1o0NQ2W00
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