keyspace: return error if the split keyspace list is empty

[JmPotato]

What problem does this PR solve?

Issue Number: Close #7101.

What is changed and how does it work?

Check List

Tests

• Unit test
• Integration test

Release note

None.

[ti-chi-bot]

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• rleungx

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[rleungx]

/merge

[ti-chi-bot]

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 075464a