Hi!

gocql.Unmarshal returns zero values, that is probably because a gocql.Unmarshaler can handle null values itself.

We can't change the behavior of MapScan as that would be backward-incompatible change. Adding a MapScanNull or similar might be possible, but we should probably do something more generic, like allowing to provide a function that is applied on every level.

There is no easy way to populate map where null is mapped to nil interface with with the current API, but it is possible.
You can provide a custom a custom unmarshaler at the top level that then recursively handles UDTs, maps, lists etc. and calls gocql.Unmarshal(customUnmarshaler(child value)) recursively. That way you propagate your custom unmarshaler down the value tree and can unmarshal in any way you want.

By the way, for query building (and mapping values to structs if you have use case for that) you might find https://github.com/scylladb/gocqlx useful.

Rather than changing the TypeInfo interface and gocql you can do this yourself if you really need it. That's what my employer does.

Your loop would instead look something like:

	for {
		rowData, err := iter.RowData()
		if err != nil {
			return nil, err
		}
		m := make(map[string]interface{}, len(columns))
		values := make([]interface{}, len(columns))
		for i, v := range rowData.Values {
			m[rowData.Columns[i]] = v
			values[i] = reflect.ValueOf(v).Addr().Interface()
		}

		if !iter.Scan(values...) {
			break
		}
		// Handle NaN values
		for key, value := range m {
			if f, ok := value.(*float64); ok && f != nil && math.IsNaN(*f) {
				m[key] = "NaN"
			}
		}
		results = append(results, m)
	}

You could even deference the values in the map after Scan but I'm not sure if that's desired or not.