Ruby-Processing and java.lang.ExceptionInInitializerError

rp5 run samples/jwishy.rb 
RubyGlobal.java:135:in `createGlobals': java.lang.ExceptionInInitializerError
    from Ruby.java:939:in `init'
    from Ruby.java:172:in `newInstance'
    from Main.java:199:in `run'
    from Main.java:110:in `run'
    from Main.java:94:in `main'

... the culprit was the alternative version of the JRE I was using (OpenJDK). After swtiching to the standard Sun JDK everything worked fine.