From eae28793262129bde83c92f5b0f4644df860f551 Mon Sep 17 00:00:00 2001
From: Arda TANRIKULU <ardatanrikulu@gmail.com>
Date: Tue, 11 May 2021 06:37:05 +0300
Subject: [PATCH] fix(merge): handle undefined interfaces array on
 ObjectTypeDefinitionNode #2629

---
 .changeset/curvy-cups-help.md                               | 5 +++++
 .../merge/src/typedefs-mergers/merge-named-type-array.ts    | 6 +++---
 2 files changed, 8 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/curvy-cups-help.md

diff --git a/.changeset/curvy-cups-help.md b/.changeset/curvy-cups-help.md
new file mode 100644
index 00000000000..d150c3c88eb
--- /dev/null
+++ b/.changeset/curvy-cups-help.md
@@ -0,0 +1,5 @@
+---
+'@graphql-tools/merge': patch
+---
+
+fix(merge): handle undefined interfaces array on ObjectTypeDefinitionNode #2629
diff --git a/packages/merge/src/typedefs-mergers/merge-named-type-array.ts b/packages/merge/src/typedefs-mergers/merge-named-type-array.ts
index f48e6676079..13b9bf8ea58 100644
--- a/packages/merge/src/typedefs-mergers/merge-named-type-array.ts
+++ b/packages/merge/src/typedefs-mergers/merge-named-type-array.ts
@@ -7,9 +7,9 @@ function alreadyExists(arr: ReadonlyArray<NamedTypeNode>, other: NamedTypeNode):
 }
 
 export function mergeNamedTypeArray(
-  first: ReadonlyArray<NamedTypeNode>,
-  second: ReadonlyArray<NamedTypeNode>,
-  config: Config
+  first: ReadonlyArray<NamedTypeNode> = [],
+  second: ReadonlyArray<NamedTypeNode> = [],
+  config: Config = {}
 ): NamedTypeNode[] {
   const result = [...second, ...first.filter(d => !alreadyExists(second, d))];
   if (config && config.sort) {