Takes a list of rows and a column and returns the max of the values under that column in
        those rows.

def max_date(self, rows: List[Row], column: DateColumn) -> Date:
        """
        Takes a list of rows and a column and returns the max of the values under that column in
        those rows.
        """
        cell_values = [row.values[column.name] for row in rows]
        if not cell_values:
            return Date(-1, -1, -1)
        if not all([isinstance(value, Date) for value in cell_values]):
            raise ExecutionError(f"Invalid values for date selection function: {cell_values}")
        return max(cell_values)