code: def check_wide_data_for_blank_choices(choice_col, wide_data):
      
      if wide_data[choice_col].isnull().any():
          msg_1 = "One or more of the values in wide_data[choice_col] is null."
          msg_2 = " Remove null values in the choice column or fill them in."
          raise ValueError(msg_1 + msg_2)
  
      return None
docs: Checks `wide_data` for null values in the choice column, and raises a
      helpful ValueError if null values are found.
  
      Parameters
      ----------
      choice_col : str.
          Denotes the column in `wide_data` that is used to record each
          observation's choice.
      wide_data : pandas dataframe.
          Contains one row for each observation. Should contain `choice_col`.
  
      Returns
      -------
      None.