public class Field<TExpression> {

    @Override
    public String toString() {
        return "Field{"
                + "name='" + name + '\''
                + ", value=" + value
                + '}';
    }
}

        public String toString() {
            return "Stage{"
                + "name='$bucketAuto'"
                + "buckets=" + buckets // the comma is missing, so the previous line is concatenated to this one without separator
                + ", groupBy=" + groupBy
                + ", options=" + options
                + '}';