Django The view didn't return an HttpResponse object. It returned None instead

Trying to check if variable 'avail.end_time:' is empty,and if so redirect to a url. But instead, I get "The view mysite.views.enter_queue didn't return an HttpResponse object. It returned None instead." ERROR

Endtime variable is being referenced from my Availabilities model where end_time = models.TimeField(null=False, blank=False)

I know this questions been asked before but none of the solutions given have helped solve the problem.

@login_required
def enter_queue(request):
# get the user from the Django request & map to variable
django_user = request.user
  #link user_profile to django users profile model & get user's profile
user_profile = django_user.profile
#user_profile = Profile.objects.get(user=request.user)
  #Map user_availabilities variable to profile from Availability model
users_availabilities = Availability.objects.filter(profile=user_profile) 
#mapping user_avail to user profile

#creating an array to store all matching sessions
all_matching_sessions = []
  # avail is each Availability object
for avail in users_availabilities:

    if avail.end_time:
        return HttpResponseRedirect(render(request,'mysite/profile.html'))
    else:
        matching_sessions = Session.objects.filter(end_time__lte=avail.end_time)#looping through all the sessions end times that match to availability
#adding them to the array
        all_matching_sessions = all_matching_sessions + matching_sessions

#If no matching sessions are available
        if len(all_matching_sessions) == 0:
    #create a session
            player_session = Session(
                game = 'random_game',
                start_time = users_availabilities[0].start_time,
                end_time = users_availabilities[0].end_time,
            )
            player_session.save()
            return  render(request, 'mysite/profile.html')

        else:
            player_session = Session(
                session = all_matching_sessions[0],
                profile = user_profile
            )
            player_session.save()
            #return HttpResponse('Waiting in queue')
            return  render(request, 'mysite/profile.html')

Image of the error for reference

**ERROR*

ValueError at /account/enter_queue/

The view mysite.views.enter_queue didn't return an HttpResponse object. It 
returned None instead.

Request Method:     GET
Request URL:    http://127.0.0.1/account/enter_queue/
Django Version:     2.0.3
Exception Type:     ValueError
Exception Value:    

The view mysite.views.enter_queue didn't return an HttpResponse object. It 
returned None instead.

Exception Location:     /usr/local/lib/python3.6/site- 
packages/django/core/handlers/base.py in _get_response, line 139
Python Executable:  /usr/local/bin/python3.6
Python Version:     3.6.4
Python Path:    

['/home/mihir/meshwell/capstone-project/siteroot',
 '/usr/local/lib/python36.zip',
 '/usr/local/lib/python3.6',
 '/usr/local/lib/python3.6/lib-dynload',
 '/usr/local/lib/python3.6/site-packages',
 '/var/www/CapstoneProject/siteroot',
 '/var/www/CapstoneProject/siteroot/mysite']

Server time:    Thu, 5 Apr 2018 04:07:23 +0000
Traceback Switch to copy-and-paste view

/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py in 
inner

                response = get_response(request)

     ...
▶ Local vars
/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py in _get_response

                    "returned None instead." % (callback.__module__, view_name)

     ...
▶ Local vars