Fixed #16552: Noted that contrib.sessions is a requirement for the admin.

    1. Add ``'django.contrib.admin'`` to your :setting:`INSTALLED_APPS`

       setting.

    2. Admin has three dependencies - :mod:`django.contrib.auth`,

       :mod:`django.contrib.contenttypes` and :mod:`django.contrib.messages`.

       If these applications are not in your :setting:`INSTALLED_APPS` list,

       add them.

    2. The admin has four dependencies - :mod:`django.contrib.auth`,

       :mod:`django.contrib.contenttypes`,

       :mod:`django.contrib.messages` and

       :mod:`django.contrib.sessions`.  If these applications are not

       in your :setting:`INSTALLED_APPS` list, add them.

    3. Add ``django.contrib.messages.context_processors.messages`` to

       :setting:`TEMPLATE_CONTEXT_PROCESSORS` and