Closure env is unit if no extra variable captured

compiler/lcalc/closure_conversion.ml

@@ -204,12 +204,14 @@ let rec transform_closures_expr :
                      [TAny, Expr.pos e]
                      (Mark.get e))
                   [
-                    Expr.etuple
-                      (List.map
-                         (fun extra_var ->
-                           Bindlib.box_var extra_var, binder_mark)
-                         extra_vars_list)
-                      m;
+                    (if extra_vars_list = [] then Expr.elit LUnit binder_mark
+                    else
+                      Expr.etuple
+                        (List.map
+                           (fun extra_var ->
+                             Bindlib.box_var extra_var, binder_mark)
+                           extra_vars_list)
+                        m);
                   ]
                   (Mark.get e);
               ])

tests/test_func/good/scope_call_func_struct_closure.catala_en

@@ -39,7 +39,6 @@ scope Foo:
 
 This test case is tricky because it creates a situation where the type of the
 two closures in Foo.r are different even with optimizations enabled.
-TODO fix this.
 
 ```catala-test-inline
 $ catala Lcalc --avoid_exceptions -O --closure_conversion -s Foo