Guard against classify nil data

test/test_classifier.rb

@@ -55,6 +55,10 @@ class TestClassifier < Test::Unit::TestCase
     assert results.first[1] < 0.5, results.first.inspect
   end
 
+  def test_instance_classify_nil
+    assert_equal [], Classifier.instance.classify(nil)
+  end
+
   def test_verify
     assert Classifier.instance.verify
   end