There is opportunity to use String.join in DescriptorSupport.toString implementation.

        for (int i=0; i < fields.length; i++) {
            if (i == (fields.length - 1)) {
                respStr = respStr.concat(fields[i]);
            } else {
                respStr = respStr.concat(fields[i] + ", ");
            }
        }

Result code is shorter and clearer.