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" 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;