Django __str__ returned non-string (type NoneType)

Question

I am getting __str__ returned non-string (type NoneType) error at edit Product Model object

Product Model

class Product(models.Model):
    ProductName = models.CharField(blank=True, max_length=250)
    Price = models.FloatField(blank=True, default=9.99)
    Tax = models.FloatField(blank=True, null=True, default=0.0)
    StoreId = models.IntegerField(blank=True, null=True)
    RelatedStore = models.ForeignKey(Store, blank=True, null=True)
    Category = models.CharField(max_length=200,
                                blank=True, null=True,
                                default='No Specific Category')
    ProductImage = models.CharField(max_length=400, null=True, blank=True)
    Features = models.TextField(blank=True, null=True)
    ProductSize = models.IntegerField(blank=True, null=True, default=3)
    FavoriteField = models.BooleanField(blank=True, default=False)
    Active = models.BooleanField(blank=True, default=True)

    def __unicode__(self):
        return self.ProductName

    def __str__(self):
        return self.ProductName

Any helpful answer will be appreciated.

Answer 1

you can try:

def __str__(self):
    return str(self.ProductName) if self.ProductName else ''

Answer 2

I little late but change the return as follows:

def __str__(self):
    return str(self.ProductName)