The first line of this method is:

    assert false;

...which makes it unusable when asserts are enabled.

Per Yegor Kozlov, "This particular assert means that SXSSFRow.getCell(int, MissingCellPolicy) is not yet covered by unit tests and *may* not be compatible with XSSF. This line will be removed in the future. Can you create a request in POI Bugzilla so that we don't forget about it?"

FWIW, I've switched to SXSSF in our application (LabKey Server) and disabled asserts, and our use of this method seems to work fine.

Workaround is to disable asserts, for example:

SXSSFRow.class.getClassLoader().setClassAssertionStatus(SXSSFRow.class.getName(), false);