Groovy compatibility broken

[Vampire]

I use this lib from Groovy and used 0.1.8 before which worked fine.
Now I updated to 0.8.2 and it is not working anymore due to https://issues.apache.org/jira/browse/GROOVY-11116.
Summarized, having an optional dependency in the signature of a method makes the class unloadable if the dependency is absent.
So currently you can only use this lib from Groovy if you have all the optional dependencies present at runtime.
Would be nice if the WebhookClientBuilder could be split into one class per optional dependency to restore Groovy compatibility.