Remove overeager null argument check, since the serialization code clearly allows a null arg. Not part of build.

extensions/xmlextras/base/src/nsDOMSerializer.cpp

@@ -160,7 +160,8 @@ nsDOMSerializer::SerializeToStream(nsIDOMNode *root,
 {
   NS_ENSURE_ARG_POINTER(root);
   NS_ENSURE_ARG_POINTER(stream);
-  NS_ENSURE_ARG_POINTER(charset);
+  // The charset arg can be null, in which case we get the document's
+  // charset and use that when serializing.
   
   nsCOMPtr<nsIDocumentEncoder> encoder;
   nsresult rv = SetUpEncoder(root,charset,getter_AddRefs(encoder));