code: def fit(self, series: np.array) -> None:
      series = self._flatten_series(series)
      self.first_train_value = series[0]
      self.last_train_value = series[-1]
      self.original_train_series = series
      self.diffed_train_series = self.diff(series)
  
file_path: lightwood/lightwood/helpers/ts.py
imports: from typing import Tuple, Dict
  from datetime import datetime
  import numpy
  import pandas
label_desc: Use image node_id 3 for calling the Differencer obj's underlying member method code with example usage: obj.fit(series) without return types