returning null for a custom scalar's serialize

[cnwangjie]

There is an old issue #1057 for that.

It has been fixed in #1104. But It does not work for now (v16.3.0).

graphql-js/src/execution/execute.ts

Lines 783 to 795 in b38429f

	function completeLeafValue(
	returnType: GraphQLLeafType,
	result: unknown,
	): unknown {
	const serializedResult = returnType.serialize(result);
	if (serializedResult == null) {
	throw new Error(
	`Expected \`${inspect(returnType)}.serialize(${inspect(result)})\` to ` +
	`return non-nullable value, returned: ${inspect(serializedResult)}`,
	);
	}
	return serializedResult;
	}

@leebyron Is it a mistake or as expected?

[cnwangjie]

Hi @IvanGoncharov,

Since this issue is unresponsive for a long time. I noticed that you are a recent committer for this project. May I ask what you think about this issue?

Due to this problem. I cannot returns a null value manually for a resolver. And the void scalar like this doesn't work.

I really hope this can be fixed if it's not intentional.

[IvanGoncharov]

@cnwangjie Spec says:
https://spec.graphql.org/draft/#sel-IANRLHHCDCECCGBke

This internal method must return a valid value for the type and not null.

"internal method" is serialize in graphql-js API.

So it's intentional.
All fields in GraphQL are nullable by default which makes it impossible to distinguish between null as GraphQL null and null produced by a scalar.
And for input types, it is even worse.

[Yifeng-Sigma]

Hey @IvanGoncharov, what's the recommended workaround for this?

[ylaguna]

@Yifeng-Sigma did you find a workaround for this?

[Yifeng-Sigma]

@Yifeng-Sigma did you find a workaround for this?

No, probably I shouldn't use scalar if it's nullable.