WIP - Null fields are ignored when scanning to a model struct

[henryjcee]

• Do only one thing
• Non breaking API changes
• [?] Tested

What did this pull request do?

We're having issues reading a row into a struct with nullable fields, represented by the guregu/null.v3 types; specifically in the case where the columns in the table have been updated from non-null to null. e.g.

err := tx.Model(target).
		WithContext(ctx).
		Where(target, "ID").
		Preload(clause.Associations).
		First(target).
		Error

In this case we'd expect the struct field to be set to null.Time{} but what we find is that the field is left unchanged. I've tracked the issue down to this commit and I can't make out what the intention of the change by looking at the previous logic:

} else if reflectV.Kind() == reflect.Ptr {
	if reflectV.IsNil() || !reflectV.IsValid() {
		field.ReflectValueOf(ctx, value).Set(reflect.New(field.FieldType).Elem())
	} else {
		return field.Set(ctx, value, reflectV.Elem().Interface())
	}
}

The commit in question mentions fixing a problem related to time fields but this block looks unrelated.

[henryjcee]

Closing this in favour of an issue now that I understand the problem