Fix walkObject to work with module namespace objects

.changeset/chilly-hairs-serve.md

@@ -0,0 +1,19 @@
+---
+'@vanilla-extract/private': patch
+---
+
+**walkObject**: Use an empty object instead of calling the input object's `constructor` when mapping over it
+
+This allows `walkObject` to be used on module namespace objects:
+
+```ts
+import * as ns from './foo';
+
+// Would sometimes cause a runtime error
+walkObject(ns, myMappingFunction);
+```
+
+The previous implementation did not work with these objects because [they do not have a `constructor` function][es6 spec].
+`esbuild` seems to have papered over this issue by providing a `constructor` function on these objects, but this seems to not be the case with `vite-node`, hence the need for this fix.
+
+[es6 spec]: https://262.ecma-international.org/6.0/#sec-module-namespace-objects

packages/private/src/walkObject.ts

@@ -11,7 +11,7 @@ export function walkObject<T extends Walkable, MapTo>(
   fn: (value: Primitive, path: Array<string>) => MapTo,
   path: Array<string> = [],
 ): MapLeafNodes<T, MapTo> {
-  const clone = obj.constructor();
+  const clone = {} as any;
 
   for (let key in obj) {
     const value = obj[key];