This is an old issue but however, recently I had the same problem using the LookupRecord processor. In my case it is due to retrieving data from the LookupRecord in which the first records appears to be null. Hence NiFi is unable to create the correct schema for this data (settings 'Inherit schema' in reader). As a result when a record with valid data is processed, NiFi seems to wrap it inside 'MapRecord'. The solution is to put the valid schema in the AvroSchemeRegistry, and provide it to the reader in your processor.   ... View more