Open all indd files from selected folder and its sub-folders

Hi all! 🙂

I have found this script written by @Kasyan Servetsky on an old post, and it's exactly what I need. However, somehow it's not working for me. When I select the folder, I get this message "Found no InDesign documents" even if there are indd files in the folder and its sub-folders. Could anyone have a look please? Thanks in advance!

var files;

var folder = Folder.selectDialog("Select a folder with InDesign documents");

if (folder != null) {

    files = GetFiles(folder);

    if (files.length > 0) {

        // turn off warnings: missing fonts, links, etc.

        app.scriptPreferences.userInteractionLevel = UserInteractionLevels.NEVER_INTERACT;

        for (i = 0; i < files.length; i++) {

            app.open(files);

        }

        // turn on warnings

        app.scriptPreferences.userInteractionLevel = UserInteractionLevels.INTERACT_WITH_ALL;

    }

    else {

        alert("Found no InDesign documents");

    }

}

function GetFiles(theFolder) {

    var files = [],

    fileList = theFolder.getFiles(),

    i, file;

    for (i = 0; i < fileList.length; i++) {

        file = fileList;

        if (file instanceof Folder) {

            files = files.concat(GetFiles(file));

        }

        else if (file instanceof File && file.name.match(/\.indd$/i)) {

            files.push(file);

        }

    }

    return files;

}