address nits

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2118,11 +2118,14 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             ),
 
             ty::Adt(def, args) => {
-                let sized_crit = def.sized_constraint(self.tcx());
-                // (*) binder moved here
-                Where(obligation.predicate.rebind(
-                    sized_crit.map_or_else(Vec::new, |ty| vec![ty.instantiate(self.tcx(), args)]),
-                ))
+                if let Some(sized_crit) = def.sized_constraint(self.tcx()) {
+                    // (*) binder moved here
+                    Where(
+                        obligation.predicate.rebind(vec![sized_crit.instantiate(self.tcx(), args)]),
+                    )
+                } else {
+                    Where(ty::Binder::dummy(Vec::new()))
+                }
             }
 
             ty::Alias(..) | ty::Param(_) | ty::Placeholder(..) => None,