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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 customer_id(self, customer_id):
 """ Sets the customer_id of this ChargeRequest. The ID of the customer to associate this transaction with. This field is required if you provide a value for `customer_card_id`, and optional otherwise. :param customer_id: The customer_id of this ChargeRequest. :type: str """


        if customer_id is None:
            raise ValueError("Invalid value for `customer_id`, must not be `None`")
        if len(customer_id) > 50:
            raise ValueError("Invalid value for `customer_id`, length must be less than `50`")

        self._customer_id = customer_id