Index: MappedNamespaceConvention.java
===================================================================
--- MappedNamespaceConvention.java	(revision 95)
+++ MappedNamespaceConvention.java	(working copy)
@@ -116,7 +116,7 @@
                     }
                 }
                 else {
-                    String strValue = (String) o;
+                    String strValue = (o == null ? null : o.toString());
                     QName name = null;
                     // note that a non-prefixed attribute name implies NO namespace,
                     // i.e. as opposed to the in-scope default namespace