Flushing a new entity fails with an exception

[mpe85]

When flushing a newly created entity there is an exception raised. Happens after upgrade to 0.20.2 (Works in 0.17.7).

Can't add a new batch because columns: STRINGS.TEXT don't have default values. DB defaults don't support in batch inserts
org.jetbrains.exposed.sql.statements.BatchDataInconsistentException: Can't add a new batch because columns: STRINGS.TEXT don't have default values. DB defaults don't support in batch inserts
	at org.jetbrains.exposed.sql.statements.BatchInsertStatement.validateLastBatch$exposed_core(BatchInsertStatement.kt:56)

I added a test that shows the problem in this PR: #760