Fix createThemeVars when using null values (#45)

Author: mattcompiles

.changeset/dirty-brooms-vanish.md

@@ -0,0 +1,6 @@
+---
+'@vanilla-extract/private': patch
+'@vanilla-extract/css': patch
+---
+
+Fix `createThemeVars` when using null values

packages/private/src/walkObject.ts

@@ -1,26 +1,37 @@
 import { MapLeafNodes } from './types';
 
-export function walkObject<T, MapTo>(
+type Primitive = string | number | null | undefined;
+
+type Walkable = {
+  [Key in string | number]: Primitive | Walkable;
+};
+
+export function walkObject<T extends Walkable, MapTo>(
   obj: T,
-  fn: (value: string | number, path: Array<string>) => MapTo,
+  fn: (value: Primitive, path: Array<string>) => MapTo,
   path: Array<string> = [],
 ): MapLeafNodes<T, MapTo> {
-  // @ts-expect-error
   const clone = obj.constructor();
 
   for (let key in obj) {
     const value = obj[key];
     const currentPath = [...path, key];
 
-    if (typeof value === 'object') {
-      clone[key] = value ? walkObject(value, fn, currentPath) : value;
-    } else if (typeof value === 'string' || typeof value === 'number') {
-      clone[key] = fn(value, currentPath);
+    if (
+      typeof value === 'string' ||
+      typeof value === 'number' ||
+      value == null
+    ) {
+      clone[key] = fn(value as Primitive, currentPath);
+    } else if (typeof value === 'object' && !Array.isArray(value)) {
+      clone[key] = walkObject(value as Walkable, fn, currentPath);
     } else {
       console.warn(
         `Skipping invalid key "${currentPath.join(
           '.',
-        )}". Should be a string, number or object. Received: "${typeof value}"`,
+        )}". Should be a string, number, null or object. Received: "${
+          Array.isArray(value) ? 'Array' : typeof value
+        }"`,
       );
     }
   }