test(chat): add test for defaulting nullable credit fields to zero

src/data/schemas/chat/unlock_private_response.ts

@@ -1,6 +1,6 @@
 import { z } from "zod";
 
-import { stringOrEmpty } from "../nullable-defaults";
+import { numberOrZero, stringOrEmpty } from "../nullable-defaults";
 import { ChatLockDetailSchema } from "./chat_payloads";
 
 /**
@@ -12,10 +12,10 @@ export const UnlockPrivateResponseSchema = z.object({
   unlocked: z.boolean(),
   content: stringOrEmpty,
   reason: UnlockPrivateReasonSchema,
-  creditBalance: z.number().default(0),
-  creditsCharged: z.number().default(0),
-  requiredCredits: z.number().default(0),
-  shortfallCredits: z.number().default(0),
+  creditBalance: numberOrZero,
+  creditsCharged: numberOrZero,
+  requiredCredits: numberOrZero,
+  shortfallCredits: numberOrZero,
   lockDetail: ChatLockDetailSchema,
 });