async getSubscriptionCreatedAttribution(subscriptionId) {
        const subscriptionCreatedEvent = await this.models.SubscriptionCreatedEvent.findOne({subscription_id: subscriptionId}, {require: false, withRelated: []});
        if (!subscriptionCreatedEvent) {
            return null;
        }
        const attribution = this.attributionBuilder.build({
            id: subscriptionCreatedEvent.get('attribution_id'),
            url: subscriptionCreatedEvent.get('attribution_url'),
            type: subscriptionCreatedEvent.get('attribution_type'),
            referrerSource: subscriptionCreatedEvent.get('referrer_source'),
            referrerMedium: subscriptionCreatedEvent.get('referrer_medium'),
            referrerUrl: subscriptionCreatedEvent.get('referrer_url')
        });
        return await attribution.fetchResource();
    }
Returns the last attribution for a given subscription ID
@param {string} subscriptionId
@returns {Promise<import('./AttributionBuilder').AttributionResource|null>}