ErrorException: [E_DEPRECATED] strtolower(): Passing null to parameter #1 ($string) of type string is deprecated

[ZixDev]

I'm using PHP 8.1.1
Server error log

• ErrorException: [E_DEPRECATED] strtolower(): Passing null to parameter #1 ($string) of type string is deprecated
• src/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/Esmtp/AuthHandler.php:256
• Generated by: Unknown account
• Jan 23, 2022 at 10:32 PM

Stack trace​

#0 [internal function]: XF::handlePhpError(8192, '[E_DEPRECATED] ...', '/Users/zix/Docu...', 256)
#1...

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