我显示子类别，但得到以下错误：
Symfony\Bridge\Doctrine\Form\ChoiceList\IdReader：：getIdValue（）：参数#1（$object）必须是类型？object，字符串给定，在C：\xampp\htdocs\demo_app\vendor\symfony\form\ChoiceList\ArrayChoiceList.php第181行调用

$formModifier = function(FormInterface $form, Category $category = null){
       
        $subCategories = null === $category ? [] : $category->getSubCategories();
        $subCategoryChoices = [];
        foreach ($subCategories as $subCategory) {
            $subCategoryChoices[$subCategory->getId()] = $subCategory->getName();
        }
        $form->add('sub_category',EntityType::class,[
            'class' => SubCategory::class,
            'choices' => $subCategoryChoices,
        ]);
    };

根据文档，如果我执行以下操作：

$formModifier = function(FormInterface $form, Category $category = null){
       
        $subCategories = null === $category ? [] : $category->getSubCategories();
        $form->add('sub_category',EntityType::class,[
            'class' => SubCategory::class,
            'choices' => $subCategories ,
        ]);
    };

我得到以下错误：

Object of class App\Entity\SubCategory could not be converted to string