Evaluating nonextant variable results into Undefined

ablescript/src/interpret.rs

@@ -539,10 +539,7 @@ impl ExecEnv {
                 kind: ErrorKind::MeloVariable(name.item.to_owned()),
                 span: name.span.clone(),
             }),
-            None => Err(Error {
-                kind: ErrorKind::UnknownVariable(name.item.to_owned()),
-                span: name.span.clone(),
-            }),
+            None => Ok(Value::Undefined),
         }
     }