There is a discrepancy when TransportExceptionInterface is thrown. Sometimes $e->getDebug() is '' and other times it contains information. Similarly, $transport->getStream()->getDebug(); sometimes returns '' because something else has already beaten you to the call...

This results in you having to do something like the following to get the debug log...

} catch (TransportExceptionInterface $e) {
    $log = $e->getDebug() ?: $transport->getStream()->getDebug();

This PR ensures that any TransportExceptionInterface thrown by send() sets the debug information. The notable case where this occurs is in handleAuth which is part of start (doHeloCommand).