code: function _doServiceCall(fileService, funcName, funcArgs) {
  		//if the function is not implemented in the file service, we throw an exception to the caller
  		if(!fileService[funcName]){
  			throw new Error(i18nUtil.formatMessage(messages["NotSupportFileSystem"], funcName));
  		}
  		return fileService[funcName].apply(fileService, funcArgs);
  	}
docs: This helper method implements invocation of the service call,
  with retry on authentication error if needed.
  @private