fix: null data unmarshal to the pointer of point should be nil

[danie1Lin]

When passing the pointer of the pointer. The pointer of the pointer will still be initialized if a null value is returned. According to the document, it should be nil. And this change include data == nil and data == []byte{} condition.

My test type

type NullTime struct {
	Time  time.Time
	Valid bool
}

func (v *NullTime) UnmarshalCQL(info gocql.TypeInfo, data []byte) error {
	var t *time.Time
	err := gocql.Unmarshal(info, data, &t)
	fmt.Println(info, "data", string(data), "time", t)
	if t == nil {
		v.Valid = false
		return nil
	} else {
		v.Time = *t
	}
	if err == nil {
		v.Time = v.Time.In(time.UTC).Truncate(time.Millisecond)
		v.Valid = true
	}
	return err
}

before the change, output:

timestamp data  time 0001-01-01 00:00:00 +0000 UTC

after change, output:

timestamp data  time <nil>

[martin-sucha]

Hi! Thanks for the pull request. Unfortunately, the proposed change is not a correct fix. It would cause even empty strings that are not null to be unmarshaled as nil into *string. Could you please open an issue and share more information to reproduce? Is the time value unmarshed from a time column or is it embedded in some user defined type or collection? Which version of gocql are you using?

[danie1Lin]

@martin-sucha Thank you. #1643. Here is the issue.