erase empty string defaultAuth from properties

[mhassan1]

This PR removes empty string defaultAuth from properties, since it confuses the connector for some MySQL servers.

Resolves https://bugs.mysql.com/bug.php?id=112931.

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[mhassan1]

I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

[mysql-oca-bot]

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bug http://bugs.mysql.com/bug.php?id=113172 for updates.
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