AllPathPermutationsGenerator() causes nullPointerException if no StopCondition is added as constructor argument

[bengchuan]

I have the model to use AllPathPermutationsGenerator() as such:

   modelhandler.add("test", new TestModel(file, true, new AllPathPermutationsGenerator(), true));

I got the following error when trying to run it:

2014-02-18 15:22:10,147 [Thread-0] ERROR org.graphwalker.Util - java.lang.NullPointerException
    at org.graphwalker.generators.PathGenerator.hasNext(PathGenerator.java:44)
    at org.graphwalker.ModelBasedTesting.hasNextStep(ModelBasedTesting.java:396)

This is caused by a the code in org.graphwalker.generators.PathGenerator:

43  public boolean More ...hasNext() {
44    return !stopCondition.isFulfilled();
45  }

stopCondition variable is not initialised when we use AllPathPermutationsGenerator without argument.