Thank you @rkrisi for fast reply.
I installed the gson jar but when trying to activate the HEOS binding in Karaf Console another package was required:
Could not resolve module: org.openhab.binding.heos [185]
Unresolved requirement: Import-Package: org.apache.commons.net.telnet; version="[3.6.0,4.0.0)
Possibly due to EHS reintegration into OH2 core now there are more dependencies.
How could I find out which add-on dependencies needs to be installed - and from where to download?
A similar discussion I found here.
Regards,
Andy