Switching to PHP 8.1 causes citeproc-php error

So, the solution is to prevent to pass NULL to the implode function analog to the Bibliography Module of D7 ( https://www.drupal.org/project/biblio/issues/3294931 🐛 PHP 8.1: Deprecated functions Needs work ). Here is the relevant part of the patch:

-    $delim = $this->delimiter;
     foreach ($this->elements as $element) {
       $text_parts[] = $element->render($data, $mode);
     }
     // Insert the delimiter if supplied.
-    $text = implode($delim, $text_parts);
+    $delimiter = isset($this->delimiter) ? $this->delimiter : "" ;
+    $text = implode($delimiter, $text_parts);

Duplicate of https://www.drupal.org/project/bibcite/issues/3323887 →

A patch for citeproc is in that issue.