Better error message

[GRbit]

Tiniest fix that will save time for someone.

I'm a newbie in Kafka, so I was sure there was something wrong with my Kafka setup, while I was decoding the topic wrong. It results in an empty topic being passed to Produce() function. The reason why I spent a few hours trying to understand what was wrong was the error messages saying Local: Invalid argument or configuration. I couldn't understand what it means and spent hours figuring out what was wrong. Hope this small change will help.

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