BUG : custom feature

If my configuration file contains

chain :
{
  ...
  s2_path : '/s2_path'
  ...
}

python_data_managing:
{
  chunk_size_mode:"split_number"
  number_of_chunks:4
  fill_missing_dates : True
  data_mode_access: "both"
}

external_features :
{
  module:"somewhere"
  functions : 'get_soi'
  concat_mode : False
  external_features_flag:True
}

and my module

def get_soi(self):
    """
    compute the Soil Composition Index
    """
    ...
    print(self.get_filled_stack())
    ...
    return coef, labels

I get the following error :

  File "soi.py", line 27, in get_soi
    print(self.get_filled_stack())
  File "custom_numpy_features.py", line 389, in get_filled_stack
    sensor.name, sensor.stack_band_position, shift)
  File "custom_numpy_features.py", line 125, in manage_raw_data
    all_dates = self.all_dates[sensor_name]
TypeError: 'NoneType' object is not subscriptable