TinyMCE error when merging two paragraph blocks

[aduth]

Issue Overview

When merging two paragraph blocks using backspace, an error is logged to the console. This does not appear to have user-impacting implications.

Steps to Reproduce (for bugs)

1. Navigate to Posts > New Post
2. Create two paragraph blocks
3. Place cursor at beginning of second paragraph block
4. Press Backspace

Expected Behavior

The two blocks are merged, and no error is logged.

Current Behavior

The two blocks are merged, but an error is logged:

Uncaught TypeError: Cannot read property 'startContainer' of null
    at Selection.getStart (tinymce.68215e08.js:29069)
    at removeCaretContainer (tinymce.68215e08.js:20275)
    at disableCaretContainer (tinymce.68215e08.js:20447)
    at Editor.<anonymous> (tinymce.68215e08.js:20473)
    at Dispatcher.fire (tinymce.68215e08.js:23089)
    at Editor.fire (tinymce.68215e08.js:23329)
    at DOMUtils.delegate (tinymce.68215e08.js:23534)
    at executeHandlers (tinymce.68215e08.js:1694)
    at HTMLParagraphElement.defaultNativeHandler (tinymce.68215e08.js:1721)

Offending line of code:

https://github.com/tinymce/tinymce/blob/1c05b6686632fca6d7ffb3983febbbcbd740efd5/src/core/main/ts/dom/Selection.ts#L145

Possible Solution

It appears that despite the instance being destroyed in the TinyMCE component's componentWillUnmount, an event callback for the keydown event is still being fired after removal.

Some possible reasons to explore:

• An asynchronous timeout is scheduled prior to the destroy, and there is no condition to check that the editor still exists after the delay elapses
• Events are not being unbound during the destroy process