title: Can not create super user, because foreign key can not be null
body: <p>How to assign foreign key value, when creating super user in Django?</p>
  <p>I want to make new superuser using python manage.py createsuperuser command, but I get an error:
  ValueError: Cannot assign &quot;&lt;QuerySet [&lt;Company: Company object (1)&gt;]&gt;&quot;: &quot;Worker.company&quot; must be a &quot;Company&quot; instance.</p>
  <p>Here is the code:</p>
  <pre><code>class CompanyAccountType(models.Model):
      accountTypeName = models.CharField(max_length=50)
      accountTypeValue = models.IntegerField()
  
  class Company(models.Model):
      city = models.ForeignKey(City, on_delete=models.RESTRICT)
      category = models.ForeignKey(Category, on_delete=models.RESTRICT)
      companyAccountType = models.ForeignKey(CompanyAccountType, on_delete=models.RESTRICT)
      
      
  class MyAccounManager(BaseUserManager):
      def create_user(self, username, password):
          user = self.model(
              username=username,
          )
          
          #I tried this for testing (real I would like to send id throught request), but I get error 
          #ValueError: Cannot assign &quot;&lt;QuerySet [&lt;Company: Company object (1)&gt;]&gt;&quot;: &quot;Worker.company&quot; must be a &quot;Company&quot; instance.
          companyObj = Company.objects.filter(id=1)
          user.company = companyObj
          
          user.set_password(password)
          user.save(using=self._db)
          return user
      
      def create_superuser(self, username, password):
          user = self.create_user(username=username, 
                              password = password,
                              )                        
          #user.company.id = 1
          user.save(using=self._db)
          return user
  
  class Worker(AbstractBaseUser):
      username = models.CharField(max_length=30, unique=True, default=&quot;user&quot;)
      password = models.CharField(max_length=300, default=&quot;password&quot;)
      company = models.ForeignKey(Company, on_delete=models.RESTRICT)  #blank=True
      workerName = models.CharField(max_length=50)
      workerProfileImage = models.ImageField(upload_to='images/', default = &quot;images/defaultUser.png&quot;, null = True)
  
      USERNAME_FIELD = 'username'
      #REQUIRED_FIELDS = ['company']
  
      objects = MyAccounManager()
  
      def __str__(self):  
          return self.username
  
      def has_perm(self, perm, obj=None):
          return True
      
      def has_module_perms(self, app_label):
          return True
  
  @receiver(post_save, sender=settings.AUTH_USER_MODEL)
  def create_auth_token(sender, instance=None, created=False, **kwargs):
      if created:
          Token.objects.create(user=instance)
  </code></pre>