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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def store(self, correlation_id, key, credential):
 """ Stores credential parameters into the store. :param correlation_id: (optional) transaction id to trace execution through call chain. :param key: a key to uniquely identify the credential parameters. :param credential: a credential parameters to be stored. """

        if credential != None:
            self._items.put(key, credential)
        else:
            self._items.remove(key)