code: func CheckNotNull(cols []*Column, row []types.Datum) error {
  	for _, c := range cols {
  		if err := c.CheckNotNull(row[c.Offset]); err != nil {
  			return err
  		}
  	}
  	return nil
  }
docs: // CheckNotNull checks if row has nil value set to a column with NotNull flag set.