              return
  
          value = data.get(field_name)
  
          if value in (None, '') and not self.blank:
              raise ValidationError('Value may not be null')
          elif value in (None, '') and self.blank:
              into[(self.source or field_name)] = None
          else:
              into[(self.source or field_name)] = self.from_native(value)
 
</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,
        if value in (None, '') and not self.null:
              return
  
          value = data.get(field_name)
  
        if value in (None, '') and not self.null:
              raise ValidationError('Value may not be null')
          elif value in (None, '') and self.blank:
              into[(self.source or field_name)] = None
          else:
              into[(self.source or field_name)] = self.from_native(value)
keep keep keep keep replace keep keep keep keep keep
 Add null related field option 
rest_framework/fields.py