From 207aea7f333f361b3b61c6cae734ca9b53fef3d8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cemalettin=20Ta=C5=9F?= <cemalettin.tas@simsoft.com.tr>
Date: Sat, 12 Dec 2020 17:46:13 +0300
Subject: [PATCH] fix(schema): Don't overwrite spec values with undefined
 (jquense/yup#1160)

---
 src/schema.ts | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/schema.ts b/src/schema.ts
index 7ffaccd91..a1006abe4 100644
--- a/src/schema.ts
+++ b/src/schema.ts
@@ -229,7 +229,14 @@ export default abstract class BaseSchema<
     let base = this;
     let combined = schema.clone();
 
-    const mergedSpec = { ...base.spec, ...combined.spec };
+    const baseSpec = { ...base.spec };
+    // only overwrite with spec values which are not undefined
+    const mergedSpec = Object.keys(combined.spec).reduce((accum, key) => {
+      if (combined.spec[key] !== undefined){
+        accum[key] = combined.spec[key]
+      }
+      return accum;
+    }, baseSpec)
 
     // if (combined.spec.nullable === UNSET)
     //   mergedSpec.nullable = base.spec.nullable;