It would be nice to represent an empty repeat-diamond "repeat while ()" like the normal default diamond symbol (like the one after the start node). I only use a label on the arrow and in this case i need to add the brackets in the statement otherwise i would get a syntax error.
@startuml
start
repeat
:read data;
:generate diagrams;
repeat while () is (test)
stop
@enduml
Thank you!