Use username in connection record, not full-blown user.

guacamole/src/main/java/net/sourceforge/guacamole/net/basic/crud/connections/List.java

@@ -155,7 +155,7 @@ public class List extends AuthenticatingHttpServlet {
                             Long.toString(record.getEndDate().getTime()));
 
                     // User involved
-                    xml.writeCharacters(record.getUser().getUsername());
+                    xml.writeCharacters(record.getUsername());
 
                     xml.writeEndElement();
                 }