// In your database/models:
type User struct {
	Name sql.NullString  // Or any other maybe/option/nullable type
}

// In your graphql schema, use this helper to define a nullable string field:
func resolveNullableString(p graphql.ResolveParams) (interface{}, error) {
	v := reflect.ValueOf(p.Source).Elem()
	if !v.IsValid() {
		return nil, fmt.Errorf("Invalid elem: %v", p.Source)
	}
	fieldName := convertFieldName(p.Info.FieldName)
	f := v.FieldByName(fieldName)
	if !f.IsValid() {
		return nil, fmt.Errorf("Missing field: %v", fieldName)
	}

	nullString := f.Interface().(sql.NullString)
	if nullString.Valid {
		return nullString.String, nil
	}

	return nil, nil
}

// You could also create other nullable types if necessary
var nullableStringField = &graphql.Field{
	Type:    graphql.String,
	Resolve: resolveNullableString,
}

// Then define your fields using that field:
fields := graphql.Fields{
	"name": nullableStringField,
}