Fix __import__("") to raise ValueError rather than return None.
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index fa36095..27f659d 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -108,6 +108,7 @@
         __import__('string')
         self.assertRaises(ImportError, __import__, 'spamspam')
         self.assertRaises(TypeError, __import__, 1, 2, 3, 4)
+        self.assertRaises(ValueError, __import__, '')
 
     def test_abs(self):
         # int