I create a basic django rest project and follow the official tutorial.  

When I called my API the following error message appears.
Am I missing some settings?

```
object of type 'type' has no len()
Request Method: GET
Request URL:    http://localhost:8000/test
Django Version: 3.0.6
Exception Type: TypeError
Exception Value:    
object of type 'type' has no len()
Exception Location: D:\Projects\PythonProjects\poeRadar\venv\lib\site-packages\rest_framework\views.py in default_response_headers, line 158
Python Executable:  D:\Projects\PythonProjects\poeRadar\venv\Scripts\python.exe
Python Version: 3.6.5

```

Here is my code  

**setting.py**

```
INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'rest_framework',
]

REST_FRAMEWORK = {
    'DEFAULT_RENDERER_CLASSES': (
        'rest_framework.renderers.JSONRenderer',
    ),
    'DEFAULT_PARSER_CLASSES': (
        'rest_framework.parsers.JSONParser',
    )
}

```

**url.py**

```
from django.conf.urls import url
from backend.api import views

urlpatterns = [
    url(r'^test$', views.test)
]

```

**views.py**

```
from rest_framework.response import Response
from rest_framework.decorators import api_view, renderer_classes
from rest_framework.renderers import JSONRenderer
import requests

@api_view(('GET',))
@renderer_classes((JSONRenderer))
def test(request):
    return Response({'a': 1})

```