      default_read_only = True  # TODO: Remove this
  
      def __init__(self, *args, **kwargs):
          self.queryset = kwargs.pop('queryset', None)
          super(RelatedField, self).__init__(*args, **kwargs)
          self.read_only = kwargs.pop('read_only', self.default_read_only)
  
      def initialize(self, parent, field_name):
          super(RelatedField, self).initialize(parent, field_name)
          if self.queryset is None and not self.read_only:
 
</s> remove         if value in (None, '') and not self.blank:
 </s> add         if value in (None, '') and not self.null: </s> remove         elif value in (None, '') and self.blank:
 </s> add         elif value in (None, '') and self.null: </s> remove             'blank': model_field.blank,
 </s> add             'null': model_field.null, </s> remove             'blank': model_field.blank,
 </s> add             'null': model_field.null,
        self.null = kwargs.pop('null', False)
      default_read_only = True  # TODO: Remove this
  
      def __init__(self, *args, **kwargs):
          self.queryset = kwargs.pop('queryset', None)
        self.null = kwargs.pop('null', False)
          super(RelatedField, self).__init__(*args, **kwargs)
          self.read_only = kwargs.pop('read_only', self.default_read_only)
  
      def initialize(self, parent, field_name):
          super(RelatedField, self).initialize(parent, field_name)
          if self.queryset is None and not self.read_only:
keep keep keep add keep keep keep keep keep keep
 Add null related field option 
rest_framework/fields.py