diff --git a/doc b/doc
index 8f85927..14b8380 160000
--- a/doc
+++ b/doc
@@ -1 +1 @@
-Subproject commit 8f859277827574f80e392d818c25dcf24afaf5b0
+Subproject commit 14b8380090858c3bed5c3b2ee7cf1408aaa133df
diff --git a/matemat/webserver/httpd.py b/matemat/webserver/httpd.py
index c59e3fc..b703f72 100644
--- a/matemat/webserver/httpd.py
+++ b/matemat/webserver/httpd.py
@@ -1,5 +1,5 @@
 
-from typing import Any, Callable, Dict, Tuple, Union
+from typing import Any, Callable, Dict, Optional, Tuple, Union
 
 import traceback
 
@@ -72,7 +72,7 @@ def pagelet(path: str):
                                     RequestArguments,
                                     Dict[str, Any],
                                     Dict[str, str]],
-                                   Tuple[int, Union[bytes, str]]]):
+                                   Tuple[int, Optional[Union[bytes, str]]]]):
         # Add the function to the dict of pagelets
         _PAGELET_PATHS[path] = fun
         # Don't change the function itself at all