stdClassのPropertyはReflectionClassで取得できない？

stdClass.php

<?php

$class = new \stdClass;
$class->key1 = 'value1';
$class->key2 = 'value2';
$class->key3 = 'value3';

$reflection = new \ReflectionClass($class);
$properties = $reflection->getProperties();

foreach ($properties as $property) {
    echo "{$property->getName()}: {$property->getValue()}\n";
}