code: def get_reference_data(
              self,
              modified_since: Optional[datetime.datetime] = None
      ) -> GetReferenceDataResponse:
          
  
          if modified_since is None:
              modified_since = datetime.datetime(year=2010, month=1, day=1)
  
          response = requests.get(
              '{}/lovs'.format(API_URL_BASE),
              headers={
                  'if-modified-since': self._format_dt(modified_since),
                  **self._get_headers(),
              },
              timeout=self._timeout,
          )
  
          if not response.ok:
              raise FuelCheckError.create(response)
  
          # return response.text
          return GetReferenceDataResponse.deserialize(response.json())
docs: Fetches API reference data.
  
          :param modified_since: The response will be empty if no
          changes have been made to the reference data since this
          timestamp, otherwise all reference data will be returned.