Index: libs/pbd/pbd/sequence_property.h
===================================================================
--- libs/pbd/pbd/sequence_property.h	(revision 12638)
+++ libs/pbd/pbd/sequence_property.h	(arbetskopia)
@@ -199,9 +199,10 @@
 		for (XMLNodeList::const_iterator j = grandchildren.begin(); j != grandchildren.end(); ++j) {
 
 			typename Container::value_type v = get_content_from_xml (**j);
-			assert (v);
-			
-			if ((*j)->name() == "Add") {
+
+			if (!v) {
+				std::cerr << "Warning undo transactions does not contain any changes." << std::endl;
+			} else if ((*j)->name() == "Add") {
 				p->_changes.added.insert (v);
 			} else if ((*j)->name() == "Remove") {
 				p->_changes.removed.insert (v);