code: @SuppressWarnings("unchecked")
  	@Override
  	public double getDelta(DATA oldDataPoint, DATA newDataPoint) {
  		if (converter == null) {
  			// In case no conversion/extraction is required, we can cast DATA to
  			// TO
  			// => Therefore, "unchecked" warning is suppressed for this method.
  			return getNestedDelta((TO) oldDataPoint, (TO) newDataPoint);
  		} else {
  			return getNestedDelta(converter.extract(oldDataPoint), converter.extract(newDataPoint));
  		}
  
  	}
docs: This method takes the two data point and runs the set extractor on it.
  The delta function implemented at {@link #getNestedDelta} is then called
  with the extracted data. In case no extractor is set the input data gets
  passes to {@link #getNestedDelta} as-is. The return value is just
  forwarded from {@link #getNestedDelta}.
  
  @param oldDataPoint
  the older data point as raw data (before extraction).
  @param newDataPoint
  the new data point as raw data (before extraction).
  @return the delta between the two points.