AttributeError: 'NoneType' object has no attribute 'tags' - upgrade Django to 1.6.5

Question

I'm trying to upgrade an old project from Django 1.4 to Django 1.7 and I'm doing it version by version. I managed to make it work fine in 1.5.8 , but on 1.6.5 I can't get past the error below (the error also appears in latest 1.7c2 ):

mod_wsgi (pid=2364): Exception occurred processing WSGI script '/home/dev/web/project_dir/wsgi/dev/dev-project-local.wsgi'.
Traceback (most recent call last):
  File "/home/dev/.envs/project_env/lib/python2.7/site-packages/django/core/handlers/wsgi.py", line 206, in __call__
    response = self.get_response(request)
  File "/home/dev/.envs/project_env/lib/python2.7/site-packages/django/core/handlers/base.py", line 146, in get_response
    response = debug.technical_404_response(request, e)
  File "/home/dev/.envs/project_env/lib/python2.7/site-packages/django/views/debug.py", line 481, in technical_404_response
    t = Template(TECHNICAL_404_TEMPLATE, name='Technical 404 template')
  File "/home/dev/.envs/project_env/lib/python2.7/site-packages/django/template/base.py", line 125, in __init__
    self.nodelist = compile_string(template_string, origin)
  File "/home/dev/.envs/project_env/lib/python2.7/site-packages/django/template/base.py", line 152, in compile_string
    parser = parser_class(lexer.tokenize())
  File "/home/dev/.envs/project_env/lib/python2.7/site-packages/django/template/base.py", line 239, in __init__
    self.add_library(lib)
  File "/home/dev/.envs/project_env/lib/python2.7/site-packages/django/template/base.py", line 353, in add_library
    self.tags.update(lib.tags)
AttributeError: 'NoneType' object has no attribute 'tags'

What can cause this error and where should I look for problems?

Using Python 2.7.3, mod_wsgi, apache.

Thanks

Answer 1

This was caused by the deprecated django.contrib.markup.templatetags.markup that my project was loading. It didn't seem to be used anywhere, so after removing it the pages started to work fine.