zadro on "[Plugin: WordPress SEO by Yoast] Failed to stop the "Google Publisher Page" empty"

Change:

echo '<link rel="publisher" href="' . esc_attr( $options['plus-publisher'] ) . '"/>' . "\n";

To:

if(substr($_SERVER['HTTP_USER_AGENT'], 0, 13) != 'W3C_Validator')
   echo '<link rel="publisher" href="' . esc_attr( $options['plus-publisher'] ) . '"/>' . "\n";
}

in frontend/class-frontend.php