Problem adding accelerator

[FredKruse]

@smehrbrodt: Thanks for your great work. It runs without problems on my machine.
I used your code as template to add a toolbar for the project I worked on (LanguageTool). I also want to add an accelerator (short key) for a service of the project. The toolbar works fine. The accelerator gets LO (6.2.8) to crash without any exception thrown (running the same method as it was added to the toolbar).
The only thing I didn't install is the RegistrationHandler. Can this be the reason for the crash? I don't understand this part of code (the methods seems to be doubled (in StarterProjectImpl and RegistrationHandler)). Could you give me any help or a hint where I have to look?
Thanks a lot