Always provide htmlentities with a string, for PHP8.1 deprecation purposes (php-debugbar#503)

Author: OdyX

src/DebugBar/DataCollector/PDO/TracedStatement.php

@@ -156,7 +156,7 @@ public function getParameters() : array
     {
         $params = [];
         foreach ($this->parameters as $name => $param) {
-            $params[$name] = htmlentities($param, ENT_QUOTES, 'UTF-8', false);
+            $params[$name] = htmlentities($param?:"", ENT_QUOTES, 'UTF-8', false);
         }
         return $params;
     }