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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 truck(self, model_mask: str = '#### @@') -> str: """Generate a truck model. :param model_mask: Mask of truck model. Here '@' is a placeholder of characters and '#' is a placeholder of digits. :return: Dummy truck model. :Example: Caledon-966O. """

        return '{}-{}'.format(
            self.random.choice(TRUCKS),
            self.random.custom_code(model_mask),
        )