From 039eedab0ac2568b5db05643a3e1bd7527574401 Mon Sep 17 00:00:00 2001
From: Tom Coleman <tom@thesnail.org>
Date: Thu, 22 Jul 2021 21:29:16 +1000
Subject: [PATCH] Don't set arg in validateOptions if it would be `undefined`.

Fixes #15630
---
 lib/client-api/src/args.test.ts | 5 +++++
 lib/client-api/src/args.ts      | 4 +++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/lib/client-api/src/args.test.ts b/lib/client-api/src/args.test.ts
index b26d877943b2..952ab73fa29f 100644
--- a/lib/client-api/src/args.test.ts
+++ b/lib/client-api/src/args.test.ts
@@ -185,6 +185,11 @@ describe('combineArgs', () => {
 });
 
 describe('validateOptions', () => {
+  // https://github.com/storybookjs/storybook/issues/15630
+  it('does not set args to `undefined` if they are unset', () => {
+    expect(validateOptions({}, { a: {} })).toStrictEqual({});
+  });
+
   it('omits arg and warns if value is not one of options', () => {
     expect(validateOptions({ a: 1 }, { a: { options: [2, 3] } })).toStrictEqual({});
     expect(once.warn).toHaveBeenCalledWith(
diff --git a/lib/client-api/src/args.ts b/lib/client-api/src/args.ts
index f09e3bf91910..85af91b9fedd 100644
--- a/lib/client-api/src/args.ts
+++ b/lib/client-api/src/args.ts
@@ -72,7 +72,9 @@ export const combineArgs = (value: any, update: any): Args => {
 export const validateOptions = (args: Args, argTypes: ArgTypes): Args => {
   return Object.entries(argTypes).reduce((acc, [key, { options }]) => {
     if (!options) {
-      acc[key] = args[key];
+      if (key in args) {
+        acc[key] = args[key];
+      }
       return acc;
     }