Existing charts have an undefined array key "subtitle"

I created a patch that should fix the problem.

Same as: https://www.drupal.org/project/charts/issues/3293577#comment-15035420 🐛 Provide the subtitle option Fixed

Here is another patch that fixes the same bug in the backend as well.

Sorry for the title changes, still have to get used to this =)

Thank you for spotting this and providing patches. I used the Null Coalescing Operator instead for consistency because that's used frequently throughout the module.

Automatically closed - issue fixed for 2 weeks with no activity.