Merge branch '5.4' into 6.0

* 5.4:
  Update routing.rst

Author: javiereguiluz

routing.rst

@@ -988,7 +988,9 @@ parameter:
 .. tip::
 
     To give a ``null`` default value to any parameter, add nothing after the
-    ``?`` character (e.g. ``/blog/{page?}``).
+    ``?`` character (e.g. ``/blog/{page?}``). If you do this, don't forget to
+    update the types of the related controller arguments to allow passing
+    ``null`` values (e.g. replace ``int $page`` by ``?int $page``).
 
 Priority Parameter
 ~~~~~~~~~~~~~~~~~~