Null support in sqlcoverage data generation.
Merge branch 'ENG-5486-null-lessthan' into ENG-5486-null-lessthan-sqlcoverage
Merge branch 'master' of github.com:VoltDB/voltdb into ENG-5486-null-lessthan-sqlcoverage
Merge branch 'ENG-5486-null-lessthan-sqlcoverage' into ENG-5486-null-lessthan