title: Cannot assign "...'": "..." must be a "User" instance
body: <p>models.py for assistance</p>
  <pre><code>class AssistanceQuest (models.Model):     
  
      Customer = models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE,blank=True,null=False)
      Status = models.BooleanField(default=False,null=False,blank=False)    
      Date_request = models.DateTimeField(auto_now_add=False)
      Tipology = models.CharField(max_length=50, null= False)
      Request = models.TextField(max_length= 1000, blank=False, null=False)
  </code></pre>
  <p>models.py for Custom User</p>
  <pre><code>from django.contrib.auth.models import AbstractUser
  from .managers import CustomUserManager
  
  class User (AbstractUser):
     is_superuser = None
     is_staff = None
     groups = None
     user_permissions = None
     objects = CustomUserManager()
  </code></pre>
  <p>manager.py for Custom User</p>
  <pre><code> from django.contrib.auth.base_user import BaseUserManager
   from django.utils.translation import ugettext_lazy as _
  
  
  class CustomUserManager(BaseUserManager):
  &quot;&quot;&quot;
  Custom user model manager senza staff o permessi
  &quot;&quot;&quot;
  def create_user(self, username,email,first_name,last_name,password):
    
      if not email:
          raise ValueError(_('The Email must be set'))
      email = self.normalize_email(email)        
      user = self.model(username = username, email = email, first_name = first_name, last_name = last_name)
      user.set_password(password)
      user.save()
      return user
  </code></pre>
  <p>and this is the view.py for the assistances</p>
  <pre><code>    if User.is_authenticated:
                  
          Message = &quot;Assistance Request From &quot; + str(User.get_full_name(User)) + &quot;: &quot;+ str(User.email)
          
        
      else:
          Message = &quot;Assistance Request From &quot; + request.POST['message-name-surname']+&quot;\n Email: &quot;+ request.POST['message-email']
      
      Message += &quot;\n City: &quot;+ request.POST['message-city']+&quot;\n Province: &quot;+ request.POST['message-province']+&quot;\n Landline Or Mobile Phone: &quot;+ request.POST['message-phone']+&quot;\n Number Order Or Purchase Period: &quot;+ request.POST['message-number-order']+&quot;\n Product Under Warranty: &quot;+ request.POST['message-warranty']+&quot;\n Request: &quot;+ request.POST['message']+&quot;\n Prefers To Be Contacted: &quot;+ request.POST['message-pref-contact']
      
      if User.is_authenticated:
          user= settings.AUTH_USER_MODEL
          Assistance = AssistanceQuest(Customer=user, Status= 'False',Request= Message, Tipology='Tecnica',Date_request=datetime.datetime.now())
          Assistance.save()
          Subject = &quot;Assistance Request From &quot; + str(User.get_username(User))
          send_mail(
              Subject,
              Message,
              'artemis.pcstore@gmail.com', 
          ['artemis.pcstore@gmail.com'],
          )
      else:
          send_mail(
              &quot;Richiesta non registrata di assistenza&quot;,
              Message,
              'artemis.pcstore@gmail.com', 
          ['artemis.pcstore@gmail.com'],
          )
  </code></pre>
  <p>When I try to insert the request, the only error i get is:
  ValueError at /Assistance/
  Cannot assign &quot;'User.User'&quot;: &quot;AssistanceQuest.Customer&quot; must be a &quot;User&quot; instance.</p>
  <p>Can someone help me?</p>