async getMemberCreatedAttribution(memberId) {
        const memberCreatedEvent = await this.models.MemberCreatedEvent.findOne({member_id: memberId}, {require: false, withRelated: []});
        if (!memberCreatedEvent) {
            return null;
        }
        const attribution = this.attributionBuilder.build({
            id: memberCreatedEvent.get('attribution_id'),
            url: memberCreatedEvent.get('attribution_url'),
            type: memberCreatedEvent.get('attribution_type'),
            referrerSource: memberCreatedEvent.get('referrer_source'),
            referrerMedium: memberCreatedEvent.get('referrer_medium'),
            referrerUrl: memberCreatedEvent.get('referrer_url')
        });
        return await attribution.fetchResource();
    }
Returns the parsed attribution for a member creation event
@param {string} memberId
@returns {Promise<import('./AttributionBuilder').AttributionResource|null>}