From 7dfaef7c96486b2a8bc23df133e3484708224dab Mon Sep 17 00:00:00 2001
From: Rikki Schulte <rikki.schulte@gmail.com>
Date: Sun, 9 Aug 2020 23:58:53 -0400
Subject: [PATCH] improvement: server only LSP bugfix for config extensions
 (#1637)

---
 .../src/GraphQLLanguageService.ts                         | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/packages/graphql-language-service-interface/src/GraphQLLanguageService.ts b/packages/graphql-language-service-interface/src/GraphQLLanguageService.ts
index cfa062cc454..fe64b8e2a7c 100644
--- a/packages/graphql-language-service-interface/src/GraphQLLanguageService.ts
+++ b/packages/graphql-language-service-interface/src/GraphQLLanguageService.ts
@@ -194,9 +194,11 @@ export class GraphQLLanguageService {
 
     // Check if there are custom validation rules to be used
     let customRules: ValidationRule[] | null = null;
-    const customValidationRules = extensions.customValidationRules;
-    if (customValidationRules) {
-      customRules = customValidationRules(this._graphQLConfig);
+    if (
+      extensions?.customValidationRules &&
+      typeof extensions.customValidationRules === 'function'
+    ) {
+      customRules = extensions.customValidationRules(this._graphQLConfig);
 
       /* eslint-enable no-implicit-coercion */
     }