Django error - 'agenda' is not a Registered namespace

Question

py apps.

from __future__ import unicode_literals

from django.apps import AppConfig

class AgendaConfig(AppConfig):
    name = 'agenda'

py.

from django.conf.urls import url
from . import views

from django.configs import DEBUG

app_name = 'agenda'
urlpatterns = [
    url(r'^$', views.AgendaView.as_view(), name='agendaview'),
]

if DEBUG:
    urlpatterns += [
        url(r'^404/$', views.handler404),
        url(r'^500/$', views.handler500),
]

py views.

from django.views.generic import TemplateView
from django.shortcuts import render

class AgendaView(TemplateView):
    template_name = 'agenda/agenda.html'

def handler404(request):
    response = render(request, '404.html', {})
    response.status_code = 404
    return response

templates/base/base.html

<li>
    <a href="{% url 'agenda:agendaview' %}">
        <i class="material-icons">&#xE878;</i>
        <span>Agenda</span>
    </a>
</li>

And when I try to execute returns me the following error:

Error during template rendering

In template /var/www/html/GetCode/templates/base/base.html, error at line 500
'agenda' is not a registered namespace

498     
499                     <li>
500                         <a href="{% url 'agenda:agendaview' %}>
501                             <i class="material-icons">&#xE878;</i>
502                             <span>Agenda</span>
503                         </a>
504                     </li>
505