Throw when <DefaultRoute> or <NotFoundRoute> have children

Fixes #677

Author: mjackson

modules/createRoutesFromReactChildren.js

@@ -104,6 +104,11 @@ function createRoute(element, parentRoute, namedRoutes) {
       'You may not have more than one <NotFoundRoute> per <Route>'
     );
 
+    invariant(
+      props.children == null,
+      '<NotFoundRoute> must not have children'
+    );
+
     parentRoute.notFoundRoute = route;
 
     return null;
@@ -121,6 +126,11 @@ function createRoute(element, parentRoute, namedRoutes) {
       'You may not have more than one <DefaultRoute> per <Route>'
     );
 
+    invariant(
+      props.children == null,
+      '<DefaultRoute> must not have children'
+    );
+
     parentRoute.defaultRoute = route;
 
     return null;