docs: def fetch_one(self, *args, **kwargs):
          """
          return one document which match the structure of the object
          `fetch_one()` takes the same arguments than the the pymongo.collection.find method.
          If multiple documents are found, raise a MultipleResultsFound exception.
          If no document is found, return None
          The query is launch against the db and collection of the object.
          """
          bson_obj = self.fetch(*args, **kwargs)
          count = bson_obj.count()
          if count > 1:
              raise MultipleResultsFound("%s results found" % count)
          elif count == 1:
              # return self(bson_obj.next(), fetched_fields=kwargs.get("projection"))
              return next(bson_obj)