def subscription(self):
        """
        Shortcut to get this customer's subscription.

        :returns: None if the customer has no subscriptions, the subscription if
            the customer has a subscription.
        :raises MultipleSubscriptionException: Raised if the customer has multiple
            subscriptions.
            In this case, use ``Customer.subscriptions`` instead.
        """

        subscriptions = self.valid_subscriptions

        if subscriptions.count() > 1:
            raise MultipleSubscriptionException(
                "This customer has multiple subscriptions. Use Customer.subscriptions "
                "to access them."
            )
        else:
            return subscriptions.first()

        Shortcut to get this customer's subscription.

        :returns: None if the customer has no subscriptions, the subscription if
            the customer has a subscription.
        :raises MultipleSubscriptionException: Raised if the customer has multiple
            subscriptions.
            In this case, use ``Customer.subscriptions`` instead.
        
djstripe/models/core.py