зачем проверять очевидные вещи?

public object this[int columnIndex] {
            get {
                DataColumn column = _columns[columnIndex];

                int record = GetDefaultRecord();
                _table.recordManager.VerifyRecord(record, this);
                VerifyValueFromStorage(column, DataRowVersion.Default, column[record]);
                return column[record];
            }
        }

public object this[DataColumn column] {
            get {
                CheckColumn(column);

                int record = GetDefaultRecord();
                _table.recordManager.VerifyRecord(record, this);
                VerifyValueFromStorage(column, DataRowVersion.Default, column[record]);
                return column[record];
            }

private void CheckColumn(DataColumn column) {
            if (column == null) {
                throw ExceptionBuilder.ArgumentNull("column");
            }
 
            if (column.Table != _table) {
                throw ExceptionBuilder.ColumnNotInTheTable(column.ColumnName, _table.TableName);
            }
        }