def METHOD_NAME(self, customer_id, association_filter_id=None):
    try:
        if customer_id is None or customer_id.strip() == "":
            raise NotFoundError()
        query_params = ""
        if association_filter_id:
            query_params = "?association_filter_id=" + association_filter_id
        response = self.config.http().get(self.config.base_merchant_path() + "/customers/" + customer_id + query_params)
        return Customer(self.gateway, response["customer"])
    except NotFoundError:
        raise NotFoundError("customer with id " + repr(customer_id) + " not found")