Cannot read property 'blockLimit' of null

[Nick]

Steps to reproduce

1. Open Source.
2. Close Source.
3. Open "Style"
4. Open Source.
5. Close Source.
6. Open "Style" (Error should happen now)

You can also see the attached video.

Expected result

Not an error.

Actual result

On Chrome you get the following error:
ckeditor.js:439 Uncaught TypeError: Cannot read property 'blockLimit' of null

Other details (browser, OS, CKEditor version, installed plugins)

• CKEditor Version: 4.5.7
• Chrome Version: 49.0.2623.87

Duplicate: #13962 (I could not find a way to open it)

[Nick]

Video of how to reproduce the issue

[Jakub Ś]

Problem can be reproduced in Blink and Webkit browsers from CKEditor 4.4.6.

NOTE: version is used to indicate when problem started occurring. Please don't change it.

[Tade0]

Git bisect revealed, that this regression was introduced with ​git:3048943550530ba2f48b43ce48939184118b34dd.

[Tade0]

One significant difference between normal operation and the bug is that at this line: ​https://github.com/ckeditor/ckeditor-dev/blob/ec85ab1687aa8ed1b892298c50db3ec4e36864d2/core/selection.js#L1483 cache.startElement is null, so it gets returned, which in turn causes problems along the way.

Another difference: Normally by the time onOpen is fired, the elements path is visible. This is not the case when the bug occurs. This is because the editor doesn't have focus at the time, which is due to the fact, that for some reason the editor.focusManager.hasFocus flag is (wrongly) truthy.

[Tade0]

One solution would be to use the editable focus state instead of the editor's, since it more reliably tells whether the editor is in the desired state.

Added unit test. Changes pushed to ​branch:t/14534.

[Jakub Ś]

We have also the same issue for IEs (including IE11 and Edge) starting from CKEditor 4.2. Please see: #12326