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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 execute_on_key(self, key, entry_processor):
 """ Applies the user defined EntryProcessor to the entry mapped by the key. Returns the object which is the result of EntryProcessor's process method. :param key: (object), specified key for the entry to be processed. :param entry_processor: (object), A stateful serializable object which represents the EntryProcessor defined on server side. This object must have a serializable EntryProcessor counter part registered on server side with the actual ``org.hazelcast.map.EntryProcessor`` implementation. :return: (object), result of entry process. """

        check_not_none(key, "key can't be None")
        key_data = self._to_data(key)
        return self._execute_on_key_internal(key_data, entry_processor)