--- a/servlib/bundling/UnknownBlockProcessor.cc	Wed May 04 15:44:40 2011 +0100
+++ b/servlib/bundling/UnknownBlockProcessor.cc	Fri May 27 18:33:25 2011 +0100
@@ -89,6 +89,8 @@
     
     // The source better have some contents, but doesn't need to have
     // any data necessarily
+if(source->contents().len() == 0)
+    ASSERT(source->contents().len() == 0);
     ASSERT(source->contents().len() != 0);
     ASSERT(source->data_offset() != 0);