title: `namedtuple_as_object` error when trying to save model Django 1.5
body: <p>I m trying to update one of the <code>int</code> field in my <code>Django</code> model.</p>
  
  <p>But I get the following error while updating this field.</p>
  
  <p>(this is using <code>python manage.py shell</code> in ipython)</p>
  
  <pre><code># this is what I m trying to do
  &gt;&gt; a = download.objects.get(id=1)
  &gt;&gt; a.url = ""
  &gt;&gt; a.save() # raises an error
  
  ---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  /usr/local/lib/python2.7/dist-packages/django/core/management/commands/shell.pyc in &lt;module&gt;()
  ----&gt; 1 a.save()
  
  /usr/local/lib/python2.7/dist-packages/django/db/models/base.pyc in save(self, force_insert, force_update, using, update_fields)
      544 
      545         self.save_base(using=using, force_insert=force_insert,
  --&gt; 546                        force_update=force_update, update_fields=update_fields)
      547     save.alters_data = True
      548 
  
  /usr/local/lib/python2.7/dist-packages/django/db/models/base.pyc in save_base(self, raw, cls, origin, force_insert, force_update, using, update_fields)
      624                         values = [(f, None, (raw and getattr(self, f.attname) or f.pre_save(self, False))) for f in non_pks]
      625                         if values:
  --&gt; 626                             rows = manager.using(using).filter(pk=pk_val)._update(values)
      627                             if force_update and not rows:
      628                                 raise DatabaseError("Forced update did not affect any rows.")
  
  /usr/local/lib/python2.7/dist-packages/django/db/models/query.pyc in _update(self, values)
      603         query.add_update_fields(values)
      604         self._result_cache = None
  --&gt; 605         return query.get_compiler(self.db).execute_sql(None)
      606     _update.alters_data = True
      607 
  
  /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.pyc in execute_sql(self, result_type)
     1012         related queries are not available.
     1013         """
  -&gt; 1014         cursor = super(SQLUpdateCompiler, self).execute_sql(result_type)
     1015         rows = cursor and cursor.rowcount or 0
     1016         is_empty = cursor is None
  
  /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.pyc in execute_sql(self, result_type)
      828         """
      829         try:
  --&gt; 830             sql, params = self.as_sql()
      831             if not sql:
      832                 raise EmptyResultSet
  
  /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.pyc in as_sql(self)
      977                 val = val.prepare_database_save(field)
      978             else:
  --&gt; 979                 val = field.get_db_prep_save(val, connection=self.connection)
      980 
      981             # Getting the placeholder for the field.
  
  /usr/local/lib/python2.7/dist-packages/django/db/models/fields/__init__.pyc in get_db_prep_save(self, value, connection)
      302         """
      303         return self.get_db_prep_value(value, connection=connection,
  --&gt; 304                                       prepared=False)
      305 
      306     def get_prep_lookup(self, lookup_type, value):
  
  /usr/local/lib/python2.7/dist-packages/jsonfield/fields.pyc in get_db_prep_value(self, value, connection, prepared)
       47         if isinstance(value, basestring):
       48             return value
  ---&gt; 49         return json.dumps(value, **self.dump_kwargs)
       50 
       51     def value_to_string(self, obj):
  
  /usr/lib/python2.7/dist-packages/simplejson/__init__.pyc in dumps(obj, skipkeys, ensure_ascii, check_circular, allow_nan, cls, indent, separators, encoding, default, use_decimal, namedtuple_as_object, tuple_as_array, **kw)
      294         namedtuple_as_object=namedtuple_as_object,
      295         tuple_as_array=tuple_as_array,
  --&gt; 296         **kw).encode(obj)
      297 
      298 
  
  TypeError: __init__() got an unexpected keyword argument 'namedtuple_as_object'
  </code></pre>
  
  <p>Can someone please suggest me, what is going wrong here?</p>