code: def resolve_one(self, correlation_id, key):
          
          connection = None
          for item in self._items:
              if item.key == key and item.connection != None:
                  connection = item.connection
                  break
          return connection
docs: Resolves a single connection parameters by its key.
  
          :param correlation_id: (optional) transaction id to trace execution through call chain.
  
          :param key: a key to uniquely identify the connection.
  
          :return: a resolved connection.