How to extract results from Redshift Data Api Query in go?

I have a sample table with this structure in Redshift:

{
ID Integer (pk)
Description Varchar NULL
}

I use Redshift Data Service to query it (api reference here). The results are of type GetStatementResultOutput which contains a property Records of type [][]type.Field. Now, this type.Field is just an interface to group all the possible field types:

// A data value in a column.
//
// The following types satisfy this interface:
//  FieldMemberBlobValue
//  FieldMemberBooleanValue
//  FieldMemberDoubleValue
//  FieldMemberIsNull
//  FieldMemberLongValue
//  FieldMemberStringValue
type Field interface {
    isField()
}

Each of those types really have a Value property that returns the value of the cell. The problem is I don't really have access to the underlying types and I have to extract the values somehow. I'm pretty new at golang and figured a way to extract the values:

type ValueExtractor struct {
        Value interface{}
    }
columnValueBytes, err := json.Marshal(columnValue)
if err != nil {
    logger.Err(err)
}
var valueEx ValueExtractor
err = json.Unmarshal(columnValueBytes, &valueEx)
// The value is here: valueEx.Value

but when the value is null a field of this type is used:

// A value that indicates whether the data is NULL.
type FieldMemberIsNull struct {
    Value bool

    noSmithyDocumentSerde
}

func (*FieldMemberIsNull) isField() {}

So my value extractor gets true instead of NULL.

What would be the appropriate way of achieving what I want?

Thank you!