  # Composite field types...
  
  class _UnvalidatedField(Field):
      def __init__(self, *args, **kwargs):
          super(_UnvalidatedField, self).__init__(*args, **kwargs)
          self.allow_blank = True
          self.allow_null = True
  
      def to_internal_value(self, data):
          return data
 
</s> remove         super(NullBooleanField, self).__init__(**kwargs)
 </s> add         super().__init__(**kwargs) </s> remove         super(PrimaryKeyRelatedField, self).__init__(**kwargs)
 </s> add         super().__init__(**kwargs) </s> remove             return super(CoreAPIClient, self).__init__(*args, **kwargs)
 </s> add             return super().__init__(*args, **kwargs) </s> remove             super(RequestsClient, self).__init__(*args, **kwargs)
 </s> add             super().__init__(*args, **kwargs) </s> remove         super(ReturnList, self).__init__(*args, **kwargs)
 </s> add         super().__init__(*args, **kwargs)
        super().__init__(*args, **kwargs)
  # Composite field types...
  
  class _UnvalidatedField(Field):
      def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
          self.allow_blank = True
          self.allow_null = True
  
      def to_internal_value(self, data):
          return data
keep keep keep keep replace keep keep keep keep keep
 Dropped Python 2 compatibility. (#6615)

Thanks to Jon Dufresne (@jdufresne) for review.

Co-authored-by: Asif Saif Uddin <auvipy@gmail.com>
Co-authored-by: Rizwan Mansuri <Rizwan@webbyfox.com> 
rest_framework/fields.py