toString() {
        const services = [];
        if (this.blob) {
            services.push("b");
        }
        if (this.table) {
            services.push("t");
        }
        if (this.queue) {
            services.push("q");
        }
        if (this.file) {
            services.push("f");
        }
        return services.join("");
    }
Converts the given services to a string.