1 files changed, 4 insertions, 2 deletions
diff --git a/src/transpile_scheme.rs b/src/transpile_scheme.rs
index ce66d10..5a88cda 100644
--- a/src/transpile_scheme.rs
+++ b/src/transpile_scheme.rs
@@ -10,8 +10,10 @@ impl TranspileScheme for ModelicaModel {
     fn repr_scheme(&self) -> Result<String, String> {
         let mut constants = vec![];
         for (c, e) in self.get_constant_vars() {
-            constants.push(format!("({} {})",
-                c, try!(e.repr_scheme())));
+            if let Some(v) = e {
+                constants.push(format!("({} {})",
+                    c, try!(v.repr_scheme())));
+            }
         }
         let mut binds = vec![];
         let mut outputs = vec![];