Notice: Undefined index: value in Drupal\views\Plugin\views\filter\NumericFilter->acceptExposedInput()

Problem/Motivation

Numeric views filter (\Drupal\views\Plugin\views\filter\NumericFilter) and all child filters (Date, SearchApiDate, etc) throw a php notice when using grouped exposed filters with a group identifier that doesn't match the filter identifier.

Notice: Undefined index: value in Drupal\views\Plugin\views\filter\NumericFilter->acceptExposedInput()

Since PHP 8 this is upgraded to an error:

TypeError: Cannot access offset of type string on string in Drupal\views\Plugin\views\filter\Date->acceptExposedInput()

Steps to reproduce

(require updates)

1. Install Drupal standard profile
2. Edit the default Content view at /admin/structure/views/view/content
3. Add a "Changed" filter
4. Select "Expose this filter to visitors, to allow them to change it"
5. Select "Grouped filters"
6. Change the "Filter identifier" value from "changed" to "date"
7. Set the Grouping 1 label to "Last week", operator to "Is greater than", value type to "An offset from ..." and value "-7 days"
8. Press Apply and then Save
9. Navigate to /admin/content
10. Set the "Changed" filter to "Last week" and press "Filter".

Proposed resolution

Update \Drupal\views\Plugin\views\filter\NumericFilter::acceptExposedInput to target the exposed group identifier as per patch in #48.

Remaining tasks

1. Add an automated test;