MINOR: Do not print an empty line when no topics exist

[KarboniteKream]

When running kafka-topics.sh --list, the command will print an empty line if no topics exist. This can cause some confusion when running with wc -l, so it's better to make sure the number of lines is zero in such a case.

This was tested against a cluster with 0 and 1+ topics to make sure the output is correct.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[divijvaidya]

Thank you for your first contribution to the project!

While the change looks good, I am afraid that changing the output format may break scripts that may be relying on the "bug" / presence of a new line.

I would be ok with this breaking change since we don't promise output compatibility of shell commands.

Let's hear what the others in the community have to say about this.

[vamossagar12]

Thanks for the PR @KarboniteKream . I agree with Divij's statement above about existing client might break. Also, there is an ongoing effort to modularize the core monolith module which also covers some of the tools related migration. As part of that, TopicCommand is also covered and there's an open PR for the same #13201

Since your PR is against master, you might want to align your PR with that PR? WDYT?

[KarboniteKream]

Sure, I understand the concerns.

you might want to align your PR with that PR?

Do you mean waiting for that PR to get merged, then rebase my changes? Or add my change to that PR?

[vamossagar12]

Sure, I understand the concerns.

you might want to align your PR with that PR?

Do you mean waiting for that PR to get merged, then rebase my changes? Or add my change to that PR?

You could wait for the PR to get merged if that's ok to you. It's your call TBH :)

[KarboniteKream]

Sure, it's no problem for me to wait. I just wanted to confirm what you had in mind.

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[KarboniteKream]

This was logging as Created topic Optional[foobar].

[KarboniteKream]

@divijvaidya @vamossagar12 I have rebased my PR now that #13201 has been merged.

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