When the globals argument to importlib.__import__() contained any value for
__package__, it was used. This was incorrect since it could be set to None to
represent the fact that a proper value was unknown. Now None will trigger the
calculation for __package__.

Discovered when running importlib against test_importhooks.
diff --git a/Misc/NEWS b/Misc/NEWS
index 6f73e73..608e9a8 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -68,6 +68,9 @@
 Library
 -------
 
+- When the globals past to importlib.__import__() has __package__ set to None,
+  fall back to computing what __package__ should be instead of giving up.
+
 - Raise a TypeError when the name of a module to be imported for
   importlib.__import__ is not a string (was raising an
   AttributeError before).