RelationManager Call to undefined method HasMany::getQualifiedRelatedKeyName

Schema::create('containers', function (Blueprint $table) {
    $table->id();

    $table->foreignId('parent_id')
        ->nullable()
        ->constrained('containers');

    $table->timestamps();
});

class Container extends Model
{
    /**
     * The parent Container this Container is stored in.
     */
    public function parent(): BelongsTo
    {
        return $this->belongsTo(self::class, 'parent_id');
    }

    /**
     * The child Containers that are stored in this Container.
     */
    public function children(): HasMany
    {
        return $this->hasMany(self::class, 'parent_id');
    }
}

class MyRelationManager extends RelationManager
{
    protected static string $relationship = 'children';

    public function table(Table $table): Table
    {
        return $table
            ->recordTitleAttribute('name')
            // ...
            ->inverseRelationship('parent');
    }
}