public static Aead create(Aead rawAead, com.google.crypto.tink.util.Bytes outputPrefix) {
    return new LegacyFullAead(rawAead, outputPrefix.toByteArray());
  }
This method covers the cases where users created their own aead/key classes.
java_src/src/main/java/com/google/crypto/tink/aead/internal/LegacyFullAead.java