title: Troubleshooting 'can only concatenate tuple (not "str") to tuple' error
body: <p>when I try to extend the django admin user. I got the following error.</p>
  
  <pre><code>can only concatenate tuple (not "str") to tuple
  </code></pre>
  
  <p>this is my models.py class</p>
  
  <pre><code>from django.db import models
  from django.contrib.auth.models import User
  from django.db.models.signals import post_save
  
  User.add_to_class('age', models.BooleanField(default=False))
  
  class Employee(models.Model):
  
    user=models.OneToOneField(User)
    name=models.CharField(max_length=100)
    address=models.CharField(max_length=200)
    designation=models.CharField(max_length=100)
    email=models.CharField(max_length=100)    
    role=models.CharField(max_length=10)  
    project=models.CharField(max_length=50)
    task=models.CharField(max_length=50)
    avatar = models.ImageField("Profile Pic", upload_to="images/", blank=True, null=True)
  
  
  
  def __unicode__(self):
  
      return self.name
  
  
  def ensure_profile_exists(sender, **kwargs):
  if kwargs.get('created', False):
      Employee.objects.create(user=kwargs.get('instance'))
  
  post_save.connect(ensure_profile_exists, sender=User)
  </code></pre>
  
  <p>this is my admin.py file</p>
  
  <pre><code>from django.contrib.auth.admin import UserAdmin
   UserAdmin.list_display += ('age')
   UserAdmin.list_filter += ('age')
   UserAdmin.fieldsets += ('age',)
  </code></pre>
  
  <p>I need to add one filed called age to the django admin user, for example first name ,last name ,email and age in personal info. please someone help me.</p>