ENG-7200 Set/alter nullability on empty table
ENG-7200 Fix TestCatalogDiffs tests
Merge branch 'master' of github.com:VoltDB/voltdb into ENG-7200-live-default-null
ENG-7200 Post-review improve messages and add test.
Merge pull request #1841 from VoltDB/ENG-7200-live-default-null

ENG-7200 live nullability changes