See https://www.postgresql.org/docs/11/datatype-oid.html, OID data type is not necessarily referring to large object, therefore it's totally OK, if there is no LargeObject mapped to the numerical value, e.g. 'table'::regclass
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Currently PostgreSQLOidDataType would fail with smth. like org.dbunit.dataset.DataSetException: org.postgresql.util.PSQLException: ERROR: large object 16548 does not exist
Thanks for the report. Please create a merge request with a proposed fix and a test that shows the problem so it stays fixed.