title: Django signals doesnt save models with custom params
body: <p>I have a custom user model <strong>CustomUser</strong> and related models <strong>Employee</strong> with Foreignkey field to user.</p>
  
  <pre><code>class Employee(models.Model):
      """Employee information."""
      user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, unique=True)
      first_name = models.CharField("first name", max_length=32, blank=True)
      last_name = models.CharField("last name", max_length=32, blank=True)
  </code></pre>
  
  <p>I try to create <strong>Employee</strong> instance after user registration using <em>post_save</em> signals with fields <em>first_name</em> and <em>last_name</em> imported from my user model fields.</p>
  
  <pre><code>@receiver(post_save, sender=CustomUser)
  def create_or_update_user_profile(sender, instance, created, **kwargs):
      if created:
          if instance.first_name and instance.last_name:
              employee = Employee.objects.create(user=instance, first_name=instance.cleaned_data['first_name'], last_name=instance.clened_data['last_name'] )
          else:
              employee = Employee.objects.create(user=instance)
  </code></pre>
  
  <p>But always created model with blank field. What is the reason for this and what needs to be changed?</p>
  
  <p>p.s. I need the same filds at both models for some reason.</p>