export null nodes (fixes a bug in portfolio model stuff)

diff --git a/src/expr/expr_template.cpp b/src/expr/expr_template.cpp
index 65a671b773e402772304bebabf8ace712d4e7b86..bc7f0f47cf8839b8f197e810cdd16fc1bd74705b 100644 (file)
--- a/src/expr/expr_template.cpp
+++ b/src/expr/expr_template.cpp
@@ -112,6 +112,7 @@ namespace expr {
 static Node exportConstant(TNode n, NodeManager* to);
 
 Node exportInternal(TNode n, ExprManager* from, ExprManager* to, ExprManagerMapCollection& vmap) {
+  if(n.isNull()) return Node::null();
   if(theory::kindToTheoryId(n.getKind()) == theory::THEORY_DATATYPES) {
     throw ExportUnsupportedException
        ("export of node belonging to theory of DATATYPES kinds unsupported");