Takes a list of rows and a column and returns the most frequent values (one or more) under
        that column in those rows.

def mode_string(self, rows: List[Row], column: StringColumn) -> List[str]:
        """
        Takes a list of rows and a column and returns the most frequent values (one or more) under
        that column in those rows.
        """
        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