diff --git a/src/Middleware/TraceMiddleware.php b/src/Middleware/TraceMiddleware.php
index e586757..bd44c80 100644
--- a/src/Middleware/TraceMiddleware.php
+++ b/src/Middleware/TraceMiddleware.php
@@ -170,6 +170,13 @@ protected function getPath(ServerRequestInterface $request): string
 
     protected function getUriMask(): array
     {
-        return is_array($this->config['uri_mask'])? $this->config['uri_mask'] : [];
+        if(
+            array_key_exists('uri_mask', $this->config) &&
+            is_array($this->config['uri_mask'])
+        ) {
+            return $this->config['uri_mask'];
+        }
+
+        return [];
     }
 }