Don't print empty operations

[sverrehu]

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Fix for #510

I only changed ExecutionPlan.java and TopicManagerTest.java. The other two files were changed due to the embedded formatter.

[purbon]

❤️ thanks a lot for your contributions @sverrehu! you guys really rock and are super helpful!

[purbon]

re: due to the embedded formatter.
I do really have to find a better way, it piss me off often this formatter :-(

[sverrehu]

❤️ thanks a lot for your contributions @sverrehu! you guys really rock and are super helpful!

I think I was the one who introduced those blank lines in the first place. ;-) But thanks!