Symfony ArrayCollection

Question

I have 2 entities: Category and Article with the following relation:

• Each Article has One Category.
• Each Category may have Many Article.

The problem :

I want to add new category using this form :

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('name', TextType::class)
        ->add('submit', SubmitType::class, [
            'label' => 'Add a new category'
        ])
    ;
}

public function configureOptions(OptionsResolver $resolver)
{
    $resolver->setDefaults([
        'data_class' => Category::class,
    ]);
}

Here's the error I get when I enter a string value in the field name:

Name Error This value should be of type array|IteratorAggregate.

I've never used ArrayCollection / Relation in symfony but I've tried to change the TextType::class to CollectionType::class it gives me a white square and I can't type anything.

In a more generic question :
How could I validate values in a form without having the error : This value should be of type array|IteratorAggregate.

Category

/**
 * @ORM\Id()
 * @ORM\GeneratedValue()
 * @ORM\Column(type="integer")
 */
private $id;

/**
 * @ORM\Column(type="string", length=255)
 * @Assert\Unique(message="Cette catégorie existe déjà")
 */
private $name;

/**
 * @return mixed
 */
public function getId()
{
    return $this->id;
}

/**
 * @return mixed
 */
public function getName()
{
    return $this->name;
}

/**
 * @param $name
 * @return Collection|null
 */
public function setName($name): ?Collection
{
    return $this->name = $name;
}

Article

/**
 * @ORM\Id()
 * @ORM\GeneratedValue()
 * @ORM\Column(type="integer")
 */
private $id;

/**
 * @ORM\Column(type="text")
 */
private $title;

/**
 * @ORM\Column(type="text")
 */
private $content;

/**
 * @ORM\Column(type="datetime")
 */
private $createdAt;

/**
 * @ORM\Column(type="string", nullable=true)
 */
private $image;

/**
 * @ORM\Column(type="datetime", nullable=true)
 */
private $editedAt;

/**
 * @ORM\ManyToOne(targetEntity="App\Entity\Category")
 */
private $category;