The "target" option must be required. If it is null, undefined, an empty string, or an empty array, then you must error.

        if (target && target.length) {
            Array.isArray(target) || (target = [target]);
            target.forEach(function (file) {
                file && targets.push(afs.resolvePath(file));
            });
        }
        if (!targets.length) {
            return callback('target must be a String or Array<String> of files');
        }