Avoid error on incorrect url
diff --git a/Allura/allura/controllers/project.py b/Allura/allura/controllers/project.py
index 1afd0e7..0260d7b 100644
--- a/Allura/allura/controllers/project.py
+++ b/Allura/allura/controllers/project.py
@@ -1019,7 +1019,10 @@
         self.neighborhood = neighborhood
 
     @expose()
-    def _lookup(self, source, *rest):
+    def _lookup(self, source=None, *rest):
+        if source is None:
+            raise exc.HTTPNotFound
+
         # iter_entry_points is a generator with 0 or 1 items, so a loop is the easiest way to handle
         for ep in iter_entry_points('allura.project_importers', source):
             return ep.load()(self.neighborhood), rest
diff --git a/Allura/allura/tests/functional/test_neighborhood.py b/Allura/allura/tests/functional/test_neighborhood.py
index bd69d8e..128afba 100644
--- a/Allura/allura/tests/functional/test_neighborhood.py
+++ b/Allura/allura/tests/functional/test_neighborhood.py
@@ -1107,5 +1107,6 @@
 
     def test_not_found(self):
         self.app.get('/p/import_project/asdf/', status=404)
+        self.app.get('/p/import_project/', status=404)
 
     # positive tests exist within ForgeImporter package