Fair enough. 

I too had a look at the code which loads it via ServiceLoader mechanism http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7-b147/javax/script/ScriptEngineManager.java#ScriptEngineManager.initEngines%28java.lang.ClassLoader%29. So the code is handling the case where a particular engine factory class isn't available and just logging the problem. 

I don't have any other concerns about this PR and it will be picked up in the next merge review queue.

Thank you for contributing the change.