Empty search results issue

in 2.1.8, we sometimes get this error in the Apache error logs when using the search with show all results:

Undefined array key “totalResults” in /plugins/site-search-360/class-sitesearch360-plugin.php on line 565

Code looks like this

    try {
        $results = $this->client->search($searchterm, $limit, $log);
    } catch (Error $e) {
        return $posts;
    }

    $totalResults = $results['totalResults'];
    if ($totalResults == 0) {
        return array();
    }

It would be better to

    $totalResults = $results['totalResults'] ?? 0;

And also other array access by key further down in the code.

– The error happens out of the blue without us touching anything.
– Reindexing the articles doesn’t fix it.
– Disabling the site-search-360 plugin fixes the issue.