--- /usr/lib/python3.5/unittest/loader.py.old	2015-10-05 18:20:44.695044469 +0200
+++ /usr/lib/python3.5/unittest/loader.py	2015-10-05 18:21:15.588855566 +0200
@@ -479,6 +479,8 @@
                     return tests, True
                 finally:
                     self._loading_packages.discard(name)
+        else:
+            return None, False
 
 
 defaultTestLoader = TestLoader()