Do not do any queries if there were no migrations before.

[Ignas]

Summary

This works around java.util.NoSuchElementException being returned by cassandra
server when executing an empty batch.

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Pull Request (PR) Checklist

Documentation

• Documentation in README.md or Wiki updated
• Update Release Notes if applicable -- collaborator-access only

Code Review

• Self code review -- take another pass through the changes yourself

Tests

• All tests passes

[hhandoko]

Thanks for your contribution @Ignas ! Before I can merge it, can you please write some test to check this condition?

[hhandoko]

This could be rewritten as if (migrationVersions.isEmpty()) return 1 guard clause.

[Ignas]

Doesn't this line prevent batch from being executed with statements return i + 1?

[hhandoko]

Hi @Ignas , can you elaborate the steps to reproduce the issue (i.e. triggering the NoSuchElementException)?

I've tried adding an empty migrations directory and no exceptions are thrown. The for-loop at for (versionRow in versionRows) { ... } and for (i in migrationVersions.indices) { ... } are skipped if no prior migrations exists or versionRows is empty.

[Ignas]

Issue #65 is resolved by the change. This can be easily reproduced with newer cassandra drivers.

[Ignas]

Ok, strike that, this does not resolve the issue, it seems that even when versions table is populated empty batch still gets executed. So the fix should instead check that batch is empty and skip it.

[Ignas]

I just removed the batch generation code, as if batch has statements in it - it does not get executed ever.

[hhandoko]

Thank you for your PR, sorry it was left open for too long!