See here for a travis build exhibiting this problem:

https://travis-ci.org/thehyve/transmart-core-db/jobs/21220075

19 tests there fail because of this problem. The culprit seems to be this line: https://github.com/thehyve/transmart-core-db/blob/5e8f0400b9ddce75e1d3d2adccf747e42bff3ee6/src/groovy/org/transmartproject/db/dataquery/clinical/TerminalConceptVariablesTabularResult.groovy#L39