From 9190e5ce1cc557931a15ca1f7b15586f033c8a02 Mon Sep 17 00:00:00 2001
From: Ginhing <3444080+Ginhing@users.noreply.github.com>
Date: Fri, 18 Feb 2022 17:15:46 +0800
Subject: [PATCH 1/2] correct outdated documentation

according #3231 returning `null` was no longer allowed.

fix prettier
---
 src/type/definition.ts | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/type/definition.ts b/src/type/definition.ts
index 090afa367f..501111c1cc 100644
--- a/src/type/definition.ts
+++ b/src/type/definition.ts
@@ -562,10 +562,9 @@ export interface GraphQLScalarTypeExtensions {
  * Scalars (or Enums) and are defined with a name and a series of functions
  * used to parse input from ast or variables and to ensure validity.
  *
- * If a type's serialize function does not return a value (i.e. it returns
+ * If a type's serialize function returns `null` or does not return a value (i.e. it returns
  * `undefined`) then an error will be raised and a `null` value will be returned
- * in the response. If the serialize function returns `null`, then no error will
- * be included in the response.
+ * in the response.
  *
  * Example:
  *

From b157d96d56ade071a24a1b0c71334efb9af57689 Mon Sep 17 00:00:00 2001
From: Ivan Goncharov <ivan.goncharov.ua@gmail.com>
Date: Mon, 21 Feb 2022 13:18:41 +0200
Subject: [PATCH 2/2] Review changes

---
 src/type/definition.ts | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/type/definition.ts b/src/type/definition.ts
index 501111c1cc..5e0c6d0472 100644
--- a/src/type/definition.ts
+++ b/src/type/definition.ts
@@ -562,9 +562,9 @@ export interface GraphQLScalarTypeExtensions {
  * Scalars (or Enums) and are defined with a name and a series of functions
  * used to parse input from ast or variables and to ensure validity.
  *
- * If a type's serialize function returns `null` or does not return a value (i.e. it returns
- * `undefined`) then an error will be raised and a `null` value will be returned
- * in the response.
+ * If a type's serialize function returns `null` or does not return a value
+ * (i.e. it returns `undefined`) then an error will be raised and a `null`
+ * value will be returned in the response. It is always better to validate
  *
  * Example:
  *
@@ -572,9 +572,16 @@ export interface GraphQLScalarTypeExtensions {
  * const OddType = new GraphQLScalarType({
  *   name: 'Odd',
  *   serialize(value) {
- *     if (value % 2 === 1) {
- *       return value;
+ *     if (!Number.isFinite(value)) {
+ *       throw new Error(
+ *         `Scalar "Odd" cannot represent "${value}" since it is not a finite number.`,
+ *       );
  *     }
+ *
+ *     if (value % 2 === 0) {
+ *       throw new Error(`Scalar "Odd" cannot represent "${value}" since it is even.`);
+ *     }
+ *     return value;
  *   }
  * });
  * ```