diff --git a/solvers/mp2nl/mp2nlmodelapi.h b/solvers/mp2nl/mp2nlmodelapi.h
index 0df2bb2eb..a53888f03 100644
--- a/solvers/mp2nl/mp2nlmodelapi.h
+++ b/solvers/mp2nl/mp2nlmodelapi.h
@@ -1541,7 +1541,8 @@ class MP2NLModelAPI
   const char* GetVarName(int v) const {
     assert(v>=0 && v<(int)var_lbs_.size());
     return
-        (int)var_names_.size() > v ? var_names_[v] : nullptr;
+        (int)var_names_.size() > v && var_names_[v]
+               ? var_names_[v] : "";
   }
 
   /// Feed extended linear part