Handle null connection and suppress exceptions in DB close method

services/nginx/app/classes/db.php

@@ -82,7 +82,14 @@ class db
 
     public function close(): void
     {
-        $this->conn->close();
+        if (!isset($this->conn)) {
+            return;
+        }
+
+        try {
+            $this->conn->close();
+        } catch (\Throwable) {
+        }
     }
 
     public function get(string $table, int $id)