Love that you've got this well covered with a test from the beginning :smile_cat: It would be good to have a test that round-trips a base64 encoded string, checking that the intermediate byte array contains the right bytes and that the round-tripped string is identical. It's possible to create Java types that look like they have the right structure but don't actually work as intended with Jackson, so a ser/deser test is good for preventing regressions.