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Solve the following problem using Python, implementing the functions described below, one line at a time
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<USER_TASK:>
Description:
 def encrypt_document(self, document_id, content, threshold=0):
 """ encrypt string data using the DID as an secret store id, if secret store is enabled then return the result from secret store encryption None for no encryption performed :param document_id: hex str id of document to use for encryption session :param content: str to be encrypted :param threshold: int :return: None -- if encryption failed hex str -- the encrypted document """

        return self._secret_store_client(self._account).publish_document(
            remove_0x_prefix(document_id), content, threshold
        )