lib/plugins/aws/provider/awsProvider.js/AwsProvider/getLogRetentionInDays
class AwsProvider:  getLogRetentionInDays() {
    if (!_.has(this.serverless.service.provider, 'logRetentionInDays')) {
      return null;
    }
    const rawRetentionInDays = this.serverless.service.provider.logRetentionInDays;
    const retentionInDays = parseInt(rawRetentionInDays, 10);
    if (_.isInteger(retentionInDays) && retentionInDays > 0) {
      return retentionInDays;
    }

    const errorMessage = `logRetentionInDays should be an integer over 0 but ${rawRetentionInDays}`;
    throw new this.serverless.classes.Error(errorMessage);
  }