Without seeing the stack trace I am assuming the npe was on the line with "model.getProtocol()".
The parser usually returns a 'null' model if the protocol was invalid in some way. Any parsing errors would be reported to the journal, but from your code it looks like you have not created a Journal. If you create an instance of this interface, and print the errors, it should help to resolve any issues.
BTW - just to let you know, there is a new effort at Imperial College to define a new version of the scribble language, which is significantly different to the one implemented in this version of the tools. So feel free to play with this version, but just be aware the next major version will be significantly different.