Add a parameter expected by mysqli_error()

extras/core.php

@@ -46,7 +46,7 @@ $result = mysqli_query($link,$sql);
 // die if SQL statement failed
 if (!$result) {
   http_response_code(404);
-  die(mysqli_error());
+  die(mysqli_error($link));
 }
 
 // print results, insert id or affected row count