title: 'RelatedManager' object has no attribute 'save' - Django
body: <p>In Django, I'm using <code>@receiver</code> to save a model object named <code>CampaignProfile</code> like so:</p>
  
  <pre><code>@receiver(post_save, sender=UserModel)
  def save_campaign(sender, instance, created, **kwargs):
      if created:
          instance.CampaignProfile.save()
  </code></pre>
  
  <p>I've created a custom user model named <code>UserModel</code> which needs to be linked with the <code>CampaignProfile</code> model, where the CampaignProfile looks something like this...</p>
  
  <pre><code>class CampaignProfile(models.Model):
      user = models.ForeignKey(UserModel, related_name='CampaignProfile', on_delete=models.CASCADE, null=True)
      campaign_title = models.CharField(max_length=50, verbose_name='Title')
  </code></pre>
  
  <p>However when I try to create a new super user through the Terminal then I get an error like so...</p>
  
  <blockquote>
    <p>AttributeError: 'RelatedManager' object has no attribute 'save'</p>
  </blockquote>
  
  <p>Does anybody know why creating a new super user would bring up this sort of error?
  Thanks.</p>