Gedmo/Doctrine Tree Extension Cannot use object as array

I’ve created an entity with a closure table and a repository alongside. I’m trying a basic example of building a tree but am seeing the error Cannot use object of type AppEntityDiscussionComment as array when calling getCommentTreeForDiscussion

Entity:

#[GedmoTree(type: 'closure')]
#[GedmoTreeClosure(class: CommentClosure::class)]
#[ORMEntity(repositoryClass: CommentRepository::class)]
#[ORMHasLifecycleCallbacks]
class Comment implements Identifiable
{
    use IdentifiableEntity;
    use TimestampableEntity;

    #[ORMColumn(type: 'text')]
    private string $content;

    #[ORMManyToOne(targetEntity: User::class)]
    #[ORMJoinColumn(nullable: false)]
    private User $author;

    #[ORMManyToOne(targetEntity: Discussion::class, inversedBy: 'comments')]
    #[ORMJoinColumn(nullable: false)]
    private Discussion $discussion;

    #[GedmoTreeParent]
    #[ORMManyToOne(targetEntity: self::class, inversedBy: 'replies')]
    #[ORMJoinColumn(referencedColumnName: 'id', nullable: true, onDelete: 'CASCADE')]
    private ?Comment $parent = null;

    #[ORMOneToMany(targetEntity: self::class, mappedBy: 'parent', cascade: ['persist', 'remove'])]
    private Collection $replies;

    #[GedmoTreeLevel]
    #[ORMColumn(type: 'integer')]
    private int $level = 0;

    #[ORMManyToMany(targetEntity: User::class)]
    #[ORMJoinTable(name: 'comment_likes')]
    private Collection $likedBy;

    // --- Getters / Setters

Closure:

#[ORMEntity]
class CommentClosure extends AbstractClosure
{
    #[ORMManyToOne(targetEntity: Comment::class)]
    #[ORMJoinColumn(name: 'ancestor', referencedColumnName: 'id', nullable: false, onDelete: 'CASCADE')]
    protected $ancestor;

    #[ORMManyToOne(targetEntity: Comment::class)]
    #[ORMJoinColumn(name: 'descendant', referencedColumnName: 'id', nullable: false, onDelete: 'CASCADE')]
    protected $descendant;
}

Repository:

class CommentRepository extends ClosureTreeRepository
{
    public function __construct(EntityManagerInterface $manager)
    {
        parent::__construct($manager, $manager->getClassMetadata(Comment::class));
    }

    public function getCommentTreeForDiscussion(Discussion $discussion): array
    {
        $roots = $this->findBy(['discussion' => $discussion, 'parent' => null], ['createdAt' => 'ASC']);

        return $this->buildTree($roots);
    }
}