code: func CanSkip(info *model.TableInfo, col *table.Column, value types.Datum) bool {
  	if col.IsPKHandleColumn(info) {
  		return true
  	}
  	if col.GetDefaultValue() == nil && value.IsNull() {
  		return true
  	}
  	if col.IsGenerated() && !col.GeneratedStored {
  		return true
  	}
  	return false
  }
docs: // CanSkip is for these cases, we can skip the columns in encoded row:
  // 1. the column is included in primary key;
  // 2. the column's default value is null, and the value equals to that;
  // 3. the column is virtual generated.