Allow renderTemplate to be called without any argument.

Author: mshima

lib/actions/fs.js

@@ -149,7 +149,7 @@ fs.existsDestination = function(filepath, ...args) {
  * @param {Object} [copyOptions] - mem-fs-editor copy options
  */
 fs.renderTemplate = function(
-  source,
+  source = '',
   destination = source,
   templateData = this._templateData(),
   templateOptions,