Micro-server is not connected if without passing anything to args

[Abbywpy]

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• 1. The issue provides a reproduction available on Github, Stackblitz or CodeSandbox

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  Please make sure the GraphQL Tools package versions under package.json matches yours.

• 2. A failing test has been provided
• 3. A local solution has been provided
• 4. A pull request is pending review

---

Describe the bug

Subschemas is stitched with gateway schema and show in schema, however the request from gateway fails and return null result.

Request from server1 success.

To Reproduce
Steps to reproduce the behavior:

Reproducible github repo link:
https://github.com/flyingmilktea/graphql-bug-reproduce/tree/62bf26617b8c187f7a182d5b8c3846d71c4182fa

::start server1
cd server1
npm i
pip install awscli aws-sam-cli
sam local start-api -t ./local.yml -l message.log --host 0.0.0.0 -p 3000

::start gateway server
cd gateway
npm i
sam local start-api -t ./local.yml -l message.log --host 0.0.0.0 -p 3001

query{
  user {
    server1Value
  }
}

Result:

{
  "data": {
    "user": null
  }
}

Expected behavior

{
  "data": {
    "user": {
      "server1Value": "User server1: 2022-06-07T04:04:46.730Z"
    }
  }
}

Environment:

• OS: Arch Linux 5.15.44-1-lts Mon, 30 May 2022 13:45:47
• "@graphql-tools/graphql-file-loader": "^7.3.14",
• "@graphql-tools/load": "^7.5.13",
• "@graphql-tools/schema": "^8.3.13",
• "@graphql-tools/stitch": "^8.6.12",
• "@graphql-yoga/node": "^2.8.0",
• "@vendia/serverless-express": "^4.8.0",
• "axios": "^0.27.2",
• "graphql-scalars": "^1.17.0",
• "lodash": "^4.17.21",
• "mem": "^8.1.1"
• NodeJS: v14.19.3

Additional context

graphql-tools/packages/stitch/src/createMergedTypeResolver.ts

Lines 5 to 61 in bccf659

	export function createMergedTypeResolver<TContext extends Record<string, any> = any>(
	mergedTypeResolverOptions: MergedTypeResolverOptions
	): MergedTypeResolver<TContext> | undefined {
	const { fieldName, argsFromKeys, valuesFromResults, args } = mergedTypeResolverOptions;
	if (argsFromKeys != null) {
	return function mergedBatchedTypeResolver(
	_originalResult,
	context,
	info,
	subschema,
	selectionSet,
	key,
	type = getNamedType(info.returnType) as GraphQLOutputType
	) {
	return batchDelegateToSchema({
	schema: subschema,
	operation: 'query' as OperationTypeNode,
	fieldName,
	returnType: new GraphQLList(type),
	key,
	argsFromKeys,
	valuesFromResults,
	selectionSet,
	context,
	info,
	skipTypeMerging: true,
	});
	};
	}
	if (args != null) {
	return function mergedTypeResolver(
	originalResult,
	context,
	info,
	subschema,
	selectionSet,
	_key,
	type = getNamedType(info.returnType) as GraphQLOutputType
	) {
	return delegateToSchema({
	schema: subschema,
	operation: 'query' as OperationTypeNode,
	fieldName,
	returnType: type,
	args: args(originalResult),
	selectionSet,
	context,
	info,
	skipTypeMerging: true,
	});
	};
	}
	return undefined;
	}

The problem could be workaround by passing undefined to args or argsFromKeys, and it's likely caused by no default case under createMergedTypeResolver for both args and argsFromKeys are null.

This may simply solve by:

const { fieldName, argsFromKeys, valuesFromResults, args= ()=>({}) } = mergedTypeResolverOptions;

Thanks @kftsehk for helping provide solution