This question already has an answer here:
What is a NullPointerException, and how do I fix it?
It's difficult to find the cause of the NPE because we do not have the whole source.
It looks like
WorldManager.init() is not called before
WorldManager.render() are called. You should put a breakpoint in
WorldManager.init() to test whether is is called before the crash.
I solved it, it wasn't feeding into the main
init() method in another class. I did manage to make some of my code more efficient though so I guess something good came out of this in the end :)