async _validateNewsletters(requestedNewsletters) {
        if (!requestedNewsletters || requestedNewsletters.length === 0) {
            return undefined;
        }

        if (requestedNewsletters.some(newsletter => !newsletter.name)) {
            return undefined;
        }

        const requestedNewsletterNames = requestedNewsletters.map(newsletter => newsletter.name);
        const requestedNewsletterNamesFilter = requestedNewsletterNames.map(newsletter => `'${newsletter.replace(/("|')/g, '\\$1')}'`);
        const matchedNewsletters = (await this._newslettersService.getAll({
            filter: `name:[${requestedNewsletterNamesFilter}]`,
            columns: ['id','name','status']
        }));

        // Check for invalid newsletters
        if (matchedNewsletters.length !== requestedNewsletterNames.length) {
            const validNewsletterNames = matchedNewsletters.map(newsletter => newsletter.name);
            const invalidNewsletterNames = requestedNewsletterNames.filter(newsletter => !validNewsletterNames.includes(newsletter));

            throw new errors.BadRequestError({
                message: tpl(messages.invalidNewsletters, {newsletters: invalidNewsletterNames})
            });
        }

        // Check for archived newsletters
        const requestedArchivedNewsletters = matchedNewsletters
            .filter(newsletter => newsletter.status === 'archived')
            .map(newsletter => newsletter.name);

        if (requestedArchivedNewsletters && requestedArchivedNewsletters.length > 0) {
            throw new errors.BadRequestError({
                message: tpl(messages.archivedNewsletters, {newsletters: requestedArchivedNewsletters})
            });
        }

        return matchedNewsletters
            .filter(newsletter => newsletter.status === 'active')
            .map(newsletter => ({id: newsletter.id}));
    }
Validates the newsletters in the request body
@param {object[]} requestedNewsletters
@param {string} requestedNewsletters[].name
@returns {Promise<object[] | undefined>} The validated newsletters