Null value for a ForeignKey field

Is it okay (possible) to have a null value for a ForeignKey field ? Sometimes the article may not be related to any product anyway.

class Product(models.Model):    
    title = models.CharField(max_length=250)
    etc etc

class Article(models.Model):
    product = models.ForeignKey(Product, null=True, blank=True, on_delete=models.CASCADE)

Yes. It’s perfectly valid to have a null ForeignKey field.