PHP warning when using arguments and previewing view without arguments

Problem/Motivation

When previewing a view display that is using this module, specifically with arguments, there is a PHP warning displayed:

Warning: Invalid argument supplied for foreach() in Drupal\entityreference_filter\Plugin\views\filter\EntityReferenceFilterViewResult->getConfiguredViewsOptions() (line 228 of modules/contrib/entityreference_filter/src/Plugin/views/filter/EntityReferenceFilterViewResult.php).

Steps to reproduce

I'm using an exposed filter and passing a contextual argument of the form #n - argument number n of the contextual filter value

The view referenced by the exposed filter has a single contextual argument and "When the filter value is NOT available" is set to "Hide the view".

Since the contextual argument in my case is "required", previewing the view display without passing an argument results in this PHP warning.

Proposed resolution

Check $results in Drupal\entityreference_filter\Plugin\views\filter\EntityReferenceFilterViewResult->getConfiguredViewsOptions() so that we don't try to foreach() on null.

Remaining tasks

Patch
Others to be determined

User interface changes

n/a

API changes

n/a

Data model changes

n/a