title: Unable to use my DRF serializers manually
body: <p>Very strange but whenever I try to use any of my DRF serializers to serialize an object, like  for instance:</p>
  
  <pre><code>me = CustomUser.objects.all()[0]
  serializer = CustomUserSerializer(me)
  
  serializer.is_valid()
  # --&gt; False
  print(serializer.errors)
  # {"non_field_errors": ["No input provided"]}
  </code></pre>
  
  <p>and this happens with totally different serializers and various objects. </p>
  
  <p>However, if I use a class-based view (that indirectly uses the same serializers and the same objects), I am able to receive a JSON response with the data serialized as expected. Said differently, calling an endpoint linked to this view</p>
  
  <pre><code>class CustomUserList(generics.ListAPIView):
      queryset = CustomUser.objects.all()
      serializer_class = CustomUserSerializer
  </code></pre>
  
  <p>will indeed return a JSON representation of all the <code>CustomUsers</code> in the database.</p>
  
  <p>There must be something I did not quite understand.</p>