persist, default aren't always booleans

lib/Properties.hs

@@ -292,7 +292,6 @@ checkObjectProperty p@(Property name _) = do
                  \either property \"bell\" or \"door\" also set."
 
   _ | name `elem` [ "default", "persist" ] -> do
-        isBool p
         suggestPropertyName' "door"
     -- extended API for doors and bells
     | name `elem` [ "openLayer", "closeLayer" ] -> do