diff --git a/src/Exception/Handler/PrettyPageHandler.php b/src/Exception/Handler/PrettyPageHandler.php
index 0710d193..5b3858d1 100644
--- a/src/Exception/Handler/PrettyPageHandler.php
+++ b/src/Exception/Handler/PrettyPageHandler.php
@@ -383,7 +383,7 @@ public function addDataTableCallback($label, /* callable */ $callback)
             throw new InvalidArgumentException('Expecting callback argument to be callable');
         }
 
-        $this->extraTables[$label] = function (\Leaf\Exceptions\Inspector $inspector = null) use ($callback) {
+        $this->extraTables[$label] = function (?\Leaf\Exceptions\Inspector $inspector = null) use ($callback) {
             try {
                 $result = call_user_func($callback, $inspector);