join() argument must be str or bytes, not 'dict'

class Product(models.Model):
    title = models.CharField(max_length=200, unique=True, verbose_name='Название')
    article = models.CharField(max_length=16, blank=True, unique=True)
    description = models.TextField(blank=True, verbose_name='Описание')
    quantity = models.PositiveIntegerField(default=0, blank=True, verbose_name='Количество')
    group = models.ForeignKey('product.ProductGroup', on_delete=models.PROTECT, null=True)
    tags = models.ManyToManyField('product.Tag')
 
class ProductGroup(models.Model):
    title = models.CharField(max_length=200, unique=True)
    code = models.CharField(max_length=200, unique=True)
    perishable = models.BooleanField(null = True)

def index(request):
    products = Product.objects.all()
    return render(request, 'product/index.html', {'products': products})
 
def categoryProducts(request, group_id):
    products = Product.objects.filter(group=group_id)
    return render(request, 'product/categoryProduct.html', {'products': products})
 
def productGroup(request):
    group = ProductGroup.objects.all()
    return render(request, 'product/categories.html', {'group': group})
 
def productDetail(request, product_id):
    product = Product.objects.get(pk=product_id)
    tags = product.tags.all()
    return render(request, 'product/detail.html', {'product': product, 'tags': tags})