Get folder ID by its name

GetFoldersByName.js

// Get the *first* folder ID by its name

function getFolderByName(folderName) {
  var folders = DriveApp.getFoldersByName(folderName);
  var folderID = null;
  if (folders.hasNext())
    folderID = folders.next();
  return folderID;
}

/*

if you have multiple folders with the same name, you would have
to iterate through them in a while loop similar to the file
iterator in the code you linked) and find a marker that proves
this is the folder you are looking for (i.e. you could have an
empty file with a particular name in there)

-- patt0
   http://stackoverflow.com/questions/20510314/find-replace-in-files-within-a-folder-using-google-apps-script

*/

This isn't working for me, it works if you change line 7 as follows: folderID = folders.next().getId();