Can't set mDistType in KNNClassifier

[benzolium]

I'm getting this error when trying to use classifier = KNNClassifier(extractors, dist='Hamming') or classifier.setDistanceMetric('Hamming')

File "/usr/lib/pymodules/python2.7/SimpleCV/MachineLearning/KNNClassifier.py", line 220, in train
    self.mClassifier.distanceContructor = orange.ExamplesDistanceConstructor_Hamming();
AttributeError: 'NoneType' object has no attribute 'distanceContructor'