Corrected default value of the DocumentType.internalSubset attribute based
on a clarification sent to the www-dom list.
diff --git a/Lib/xml/dom/minidom.py b/Lib/xml/dom/minidom.py
index 628a375..97d622f 100644
--- a/Lib/xml/dom/minidom.py
+++ b/Lib/xml/dom/minidom.py
@@ -727,7 +727,7 @@
     name = None
     publicId = None
     systemId = None
-    internalSubset = ""
+    internalSubset = None
     entities = None
     notations = None