If it’s a BLOB as output JDBC type, the output field type should be byte Array to make it serializable.
All objects which exist in the pipeline must be encoded into a binary format (i.e. serialized).
To resolve the issue, change the “Output Field Type” of the adapter service from java.sql.Blob to “byte array”. The resulting output filed will then be passed to a flow service as a byte array.
Referenced from my old post.