'NoneType' object does not support item assignment in nav-cta.html in the pattern-library

[MugoBrian]

Issue:
When accessing the nav-cta in the pattern-library. It returns the following error (See screenshot below).

Steps To Reproduce The Error:
Start the wagtail.org server
Access the /pattern-library/pattern/patterns/components/nav-cta/nav-cta.html route

Environment Used:
The issue occurs in both of these environments both using Docker and Chrome Browser Version 118.0.5993.117 (Official Build) (64-bit):

Gitpod
Locally (Ubuntu 22.0.4)