code: def mode_string(self, rows: List[Row], column: StringColumn) -> List[str]:
          
          most_frequent_list = self._get_most_frequent_values(rows, column)
          if not most_frequent_list:
              return []
          if not all([isinstance(value, str) for value in most_frequent_list]):
              raise ExecutionError(f"Invalid values for mode_string: {most_frequent_list}")
          return most_frequent_list
docs: Takes a list of rows and a column and returns the most frequent values (one or more) under
          that column in those rows.