[6.x]: Blank headings on entries sidebar

[DenyEs]

What happened?

Description

When you leave a blank heading on a sidebar in Entries section, it triggers an error

Twig\Error\RuntimeError
vendor/craftcms/cms/resources/templates/_elements/sources.twig:86

Key "heading" for sequence/mapping with keys "key, page, type" does not exist in "_elements/sources" at line 86. 

Steps to reproduce

1. Create a new section
2. Go to entries
3. Re-order as you wish and leave a blank heading

Expected behavior

Page loads up with all entries

Actual behavior

Triggers an error and makes the whole Entries section inaccessible

Craft CMS version

6.0.0-alpha2

PHP version

8.5

Operating system and version

macOS 26.5

Database type and version

8.4.6

Image driver and version

No response

Installed plugins and versions

No response

[linear-code]

CMS-2095

[DenyEs]

I created a pull request for this as it's fixed it on my local copy if that helps - #18890

[brandonkelly]

Craft 6.0.0-alpha.3 is out with a fix for this. Thanks for reporting!