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(index=col.index)
          out[self.col_name] = col.fillna(self.default_value)
          out[self.new_name] = (pd.notnull(col) * 1).astype(int)
          return out