TypeError during blur event in WYSIWYG mode

Describe the bug

An error occurs inside toastui-editor.js when the editor loses focus (blur event). This only happens in WYSIWYG mode (initialEditType: 'wysiwyg'). With initialEditType: 'markdown' there's no error during handling of the blur event.

This error is logged in the browser console:

TypeError: "dom.getParentUntil(...) is undefined"
    fixIMERange https://uicdn.toast.com/editor/latest/toastui-editor-all.js:26833
    _initSquireEvent https://uicdn.toast.com/editor/latest/toastui-editor-all.js:26074
    fireEvent https://uicdn.toast.com/editor/latest/toastui-editor-all.js:12467
    handleEvent https://uicdn.toast.com/editor/latest/toastui-editor-all.js:12467

As a result, the registered event handler for the blur event is not called. The editor itself still works perfectly after the error occurred.

To Reproduce

I created this minimal HTML+JS to reproduce the error:

<html>
<head>
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.48.4/codemirror.min.css" />
    <link rel="stylesheet" href="toastui-editor.css" />
</head>
<body>
    <div id="xxeditor"></div>
    <script src="https://uicdn.toast.com/editor/latest/toastui-editor-all.js"></script>
    <script>
        const editor = new toastui.Editor({
            el: document.querySelector('#xxeditor'),
            height: '500px', 
            initialEditType: 'wysiwyg',
            initialValue: '# This is MarkDown\n\nHello World!',
            events: {
                blur: function() {
                    console.log('blur!');
                }
            }
        });

        // BTW: same thing happens when registering the event handler with addHook()
        // editor.addHook("blur", function(e) {
        //  console.log("blur!");
        // });
    </script>
</body>
</html>

After loading the page do this to reproduce:

click somewhere inside the editor control (focus)
click somewhere outside the editor control (blur)

Expected behavior

There should be no error and the registered event handler for the blur event should be called.

Desktop (please complete the following information):

OS: Linux
Browser: Firefox, Chromium
Version: latest versions, 64-Bit

Additional context

Thanks a lot for all of your hard work on this project. This is really an amazing editor :1st_place_medal:.

nhn / tui.editor