ORA 01400: cannot insert NULL into (STAT.CSR_MIGRATION_LOG.MIGR_ROW_ID) (4256103)

Run the query below to make sure trigger CSR_MIGRATION_LOG_TRG1 does exist. 

1. SELECT CSR_MIGR_LOG_MIGR_ROW_ID_SEQ1.NEXTVAL FROM DUAL

2. ALTER TRIGGER CSR_MIGRATION_LOG_TRG1 ENABLE)

If the sequence and trigger does not exist then check the upgrade log. The export of the stat db for the upgrade might be missing the trigger or the upgrade process encounter some errors. In this case, it is suggested to do the upgrade over since we are not sure what other data might be missing in the stat db.