Django import export has error "Tablib has no format 'None' or it is not registered"

I am trying to implement csv import in my application and I have this error, Tablib has no format 'None' or it is not registered.

I am using python 3.5 and Django 2.2. I tried the same code with python 2.7 with Django 1.8 and it worked well. Is there any problem with my code?

My model:

class Stock(models.Model):
    category = models.ForeignKey(Category, on_delete=models.CASCADE, blank=True)
    item_name = models.CharField(max_length=50, blank=True, null=True)
    quantity = models.IntegerField(default='0', blank=False, null=True)
    receive_quantity = models.IntegerField(default='0', blank=True, null=True)
    receive_by = models.CharField(max_length=50, blank=True, null=True)
    issue_quantity = models.IntegerField(default='0', blank=True, null=True)
    issue_by = models.CharField(max_length=50, blank=True, null=True)
    issue_to = models.CharField(max_length=50, blank=True, null=True)
    phone_number = models.CharField(max_length=50, blank=True, null=True)
    created_by = models.CharField(max_length=50, blank=True, null=True)
    reorder_level = models.IntegerField(default='0', blank=True, null=True)
    last_updated = models.DateTimeField(auto_now_add=False, auto_now=True)

    def __str__(self):
        return self.item_name

Resources.py

from import_export import resources
from .models import Stock, Person

class StockResource(resources.ModelResource):
    class Meta:
        model = Stock

Views.py:

from .resources import StockResource


def upload(request):
    if request.method == 'POST':
        stock_resource = StockResource()
        dataset = Dataset()
        new_stock = request.FILES['myfile']

        imported_data = dataset.load(new_stock.read())
        result = stock_resource.import_data(dataset, dry_run=True)  # Test data import

        if not result.has_errors():
            stock_resource.import_data(dataset, dry_run=False)  # Run import

    return render(request, 'csv_import.html')

csv_import.html

    <form method="post" enctype="multipart/form-data">
      {% csrf_token %}
      <input type="file" name="myfile"><br><br>
      <button type="submit">Upload</button>
    </form>

csv_import.csv

1,phone,1,0,9,0,9,9,9,,ssaine,0,2020-06-11,
2,computer,2,0,9,0,9,9,9,9,ssaine,0,2020-08-11,