title: create method is raising key error in serializer
body: <p>I am creating an API for signup.</p>
  
  <p>Serializers.py</p>
  
  <pre><code>class UserSignupSerializer(serializers.Serializer):
  
  
  class Meta:
      model = User
      fields = ['username', 'first_name', 'last_name', 'email', 'role']
      extra_kwargs = {'password': {'write_only': True}}
  
  def create(self, validate_data):
  
      user = User.objects.create(email=validate_data['email'], first_name=validate_data['first_name'],last_name=validate_data['last_name'], role='user', username=validate_data['username'])
      user.set_password(validate_data['password'])
  
      user.save()
      return user
  </code></pre>
  
  <p>Views.py</p>
  
  <pre><code>class UserSignupView(APIView):
      def post(self, request):
          serializer = UserSignupSerializer(data=request.data)
          if serializer.is_valid():
              serializer.save()
              return Response(serializer.data, status=status.HTTP_201_CREATED)
          else:
              return Response(status=status.HTTP_204_NO_CONTENT)
  </code></pre>
  
  <p>But this is giving key error 'email' or anything I put first in this line:</p>
  
  <pre><code>user = User.objects.create(email=validate_data['email'], first_name=validate_data['first_name'],last_name=validate_data['last_name'], role='user', username=validate_data['username'])
  </code></pre>
  
  <p><strong>Edit</strong>
  Error</p>
  
  <pre><code>Internal Server Error: /api/user_signup/
  Traceback (most recent call last):
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
      response = get_response(request)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
      response = self.process_exception_by_middleware(e, request)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
      response = wrapped_callback(request, *callback_args, **callback_kwargs)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
      return view_func(*args, **kwargs)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\views\generic\base.py", line 71, in view
      return self.dispatch(request, *args, **kwargs)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\views.py", line 497, in dispatch
      response = self.handle_exception(exc)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\views.py", line 457, in handle_exception
      self.raise_uncaught_exception(exc)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\views.py", line 468, in raise_uncaught_exception
      raise exc
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\views.py", line 494, in dispatch
      response = handler(request, *args, **kwargs)
    File "D:\Django\FitnessProject\FitnessApp\fitness_api\views.py", line 187, in post
      serializer.save()
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\serializers.py", line 213, in save
      self.instance = self.create(validated_data)
    File "D:\Django\FitnessProject\FitnessApp\fitness_api\serializers.py", line 85, in create
      user = User.objects.create(email=validate_data['email'], first_name=validate_data['first_name'],last_name=validate_data['last_name'], role='user', username=validate_data['username'])
  KeyError: 'email'
  [2019-09-03 11:49:43,186] log: ERROR - Internal Server Error: /api/user_signup/
  Traceback (most recent call last):
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
      response = get_response(request)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
      response = self.process_exception_by_middleware(e, request)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
      response = wrapped_callback(request, *callback_args, **callback_kwargs)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
      return view_func(*args, **kwargs)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\django\views\generic\base.py", line 71, in view
      return self.dispatch(request, *args, **kwargs)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\views.py", line 497, in dispatch
      response = self.handle_exception(exc)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\views.py", line 457, in handle_exception
      self.raise_uncaught_exception(exc)
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\views.py", line 468, in raise_uncaught_exception
      raise exc
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\views.py", line 494, in dispatch
      response = handler(request, *args, **kwargs)
    File "D:\Django\FitnessProject\FitnessApp\fitness_api\views.py", line 187, in post
      serializer.save()
    File "D:\django\FitnessProject\fitness_venv\lib\site-packages\rest_framework\serializers.py", line 213, in save
      self.instance = self.create(validated_data)
    File "D:\Django\FitnessProject\FitnessApp\fitness_api\serializers.py", line 85, in create
      user = User.objects.create(email=validate_data['email'], first_name=validate_data['first_name'],last_name=validate_data['last_name'], role='user', username=validate_data['username'])
  KeyError: 'email'
  [03/Sep/2019 11:49:43] "POST /api/user_signup/?username=user_4&amp;last_name=user&amp;first_name=user&amp;email=u@gmail.com&amp;password=user&amp;role=user HTTP/1.1" 500 18553
  </code></pre>