### Question:
RollingMeanEnricher extends AbstractTypeTransformingEnricher<T,Double> { public Double getAverage() { pruneValues(); return values.size() == 0 ? null : sum(values) / values.size(); } RollingMeanEnricher();  RollingMeanEnricher(Entity producer, AttributeSensor<T> source, AttributeSensor<Double> target,
            int windowSize); Double getAverage(); @Override void onEvent(SensorEvent<T> event);  }### Answer:
@Test public void testDefaultAverage() { assertEquals(averager.getAverage(), null); }