Hello E.,
From:
For a dot, You can use interface as:
@startuml
object parent
() " " as helper
parent <|-- helper
helper -- child1
helper -- child2
helper -- child3
@enduml
And if we make the diamond invisible, we make a missing element or a hole appear on the diagram...
@startuml
<style>
diamond {
Backgroundcolor transparent
Linecolor transparent
}
</style>
object parent
<> helper
parent <|-- helper
helper -- child1
helper -- child2
helper -- child3
@enduml
If that can help,
Regards,
Th.