docs: def transform(self, col):
          """Prepare the transformer to convert data and return the processed table.
  
          Args:
              col(pandas.DataFrame): Data to transform.
  
          Returns:
              pandas.DataFrame
          """
  
          out = pd.DataFrame()
  
          # Make sure all nans are handled the same by replacing with None
          column = col[self.col_name].replace({np.nan: None})
          out[self.col_name] = column.apply(self.get_val)
  
          return out