Merged revisions 74584 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/branches/py3k

........
  r74584 | brett.cannon | 2009-08-29 20:47:36 -0700 (Sat, 29 Aug 2009) | 3 lines

  Have importlib raise ImportError if None is found in sys.modules. This matches
  current import semantics.
........

Lib/importlib/_bootstrap.py

@@ -860,7 +860,12 @@ def _gcd_import(name, package=None, level=0):
             name = package[:dot]
     with _ImportLockContext():
         try:
-            return sys.modules[name]
+            module = sys.modules[name]
+            if module is None:
+                message = ("import of {} halted; "
+                            "None in sys.modules".format(name))
+                raise ImportError(message)
+            return module
         except KeyError:
             pass
         parent = name.rpartition('.')[0]