Migration panic: `cannot write NULL to non-NULL field`

https://dolthub-preview-1.awsdev.ld-corp.com/repositories/dolthub/corona-virus-state-action/jobs/bdf73f9f-8e44-40c2-9d6f-23d07252639b?refName=master

```job failed: failed to migrate: failed to migrate: panic: cannot write NULL to non-NULL field [recovered]
panic: Tuple(34, "AK", 35, "primary_election")
goroutine 6827 [running]:
github.com/dolthub/dolt/go/libraries/doltcore/migrate.translator.TranslateTuple.func2()
/src/libraries/doltcore/migrate/tuples.go:118 +0x79
panic({0x1be7e60, 0x2355260})
/usr/local/go/src/runtime/panic.go:884 +0x212
github.com/dolthub/dolt/go/store/val.(*TupleBuilder).Build(0xc007115c58?, {0x236b5f0?, 0x33dbc80?})
/src/store/val/tuple_builder.go:58 +0x85
github.com/dolthub/dolt/go/libraries/doltcore/migrate.translator.TranslateTuple({0xc005f32b00, 0xc005e7ff50, {0x237f130, 0xc0010e2000}, {0x236b5f0, 0x33dbc80}}, {0x2375878?, 0xc003ba1780?}, {{{0x2375f78, 0xc0001fe000}, ...}})
/src/libraries/doltcore/migrate/tuples.go:122 +0x4a5
github.com/dolthub/dolt/go/libraries/doltcore/migrate.translateTuples({0x2375878, 0xc003ba1780}, {0xc005f32b00, 0xc005e7ff50, {0x237f130, 0xc0010e2000}, {0x236b5f0, 0x33dbc80}}, {0xc005f32b80, 0xc005e7fd10, ...}, ...)
/src/libraries/doltcore/migrate/transform.go:666 +0x439
github.com/dolthub/dolt/go/libraries/doltcore/migrate.migrateIndex.func2()
/src/libraries/doltcore/migrate/transform.go:618 +0xcd
golang.org/x/sync/errgroup.(*Group).Go.func1()
/go/pkg/mod/golang.org/x/sync@v0.1.0/errgroup/errgroup.go:75 +0x64
created by golang.org/x/sync/errgroup.(*Group).Go
/go/pkg/mod/golang.org/x/sync@v0.1.0/errgroup/errgroup.go:72 +0xa5```