code: def fft_aggregated(self, x, param=None):
          
          if param is None:
              param = [{'aggtype': 'centroid'}]
          _fft_agg = feature_calculators.fft_aggregated(x, param)
          logging.debug("fft aggregated by tsfresh calculated")
          return list(_fft_agg)
docs: As in tsfresh `fft_aggregated <https://github.com/blue-yonder/tsfresh/blob/master/tsfresh/feature_extraction/\
          feature_calculators.py#L896>`_
  
          Returns the spectral centroid (mean), variance, skew, and kurtosis of the absolute fourier transform spectrum.
          
          :param x: the time series to calculate the feature of
          :type x: pandas.Series
          :param param: contains dictionaries {"aggtype": s} where s str and in ["centroid", "variance",
              "skew", "kurtosis"]
          :type param: list
          :return: the different feature values
          :rtype: pandas.Series