Mongos count command should report errors in errmsg field, not cause field

Fatal error: Uncaught exception 'MongoDB\Driver\Exception\ConnectionException' with message 'failed on : shard0000' in app/vendor/composer/mongodb/mongodb/src/Operation/Count.php:111

Stack trace:

#0 app/vendor/composer/mongodb/mongodb/src/Operation/Count.php(111): MongoDB\Driver\Server->executeCommand('keywords', Object(MongoDB\Driver\Command), Object(MongoDB\Driver\ReadPreference))

#1 app/vendor/composer/mongodb/mongodb/src/Collection.php(233): MongoDB\Operation\Count->execute(Object(MongoDB\Driver\Server))

#2 app/scratch08.php(20): MongoDB\Collection->count(Array, Array)

#3 {main}

  thrown in app/vendor/composer/mongodb/mongodb/src/Operation/Count.php on line 111

$manager = new MongoDB\Driver\Manager("mongodb://localhost:27017");

$col = new \MongoDB\Collection($manager, 'keywords', 'keywords');

$res = $col->count(

    [

        '_id' => [

            '$in' => []

        ]

    ],

    [

        'hint' => [

            '_not_exists' => 1

        ]

    ]

);