Fix filling-in-missing-data.md example code

[ntf]

I come across this feature today when I was trying to fix a partial rendering behavior in my app.

I thought any query on node(id: ID) would re-use the cache on the store and perform partial rendering by default, but it seems that it is not the case.

For the code snippet below, it seems that the return value for "Not handled" should be undefined rather than null

const missingFieldHandlers = [
    {
        handle(field, record, argValues) {
            if (
                record != null &&
                record.__typename === ROOT_TYPE &&
                field.name === 'node' &&
                argValues.hasOwnProperty('id')
            ) {
                // If field is node(id: $id), look up the record by the value of $id
                return argValues.id;
            }

            // should return undefined instead of null if this handle function does not handle the given inputs.
            return undefined; 
        },
        kind: 'linked',
    }
];

According to this:

relay/packages/relay-runtime/store/DataChecker.js

Lines 275 to 286 in 9d0e3ad

	const newValue = handler.handle(
	field,
	record,
	args,
	this._recordSourceProxy,
	);
	if (
	newValue !== undefined &&
	(newValue === null || this._mutator.getStatus(newValue) === EXISTENT)
	) {
	return newValue;
	}

If the return value is null, here

relay/packages/relay-runtime/store/DataChecker.js

Lines 553 to 558 in 9d0e3ad

	linkedID = this._handleMissingLinkField(field, dataID);
	if (linkedID != null) {
	this._mutator.setLinkedRecordID(dataID, storageKey, linkedID);
	} else if (linkedID === null) {
	this._mutator.setValue(dataID, storageKey, null);
	}

sets the value to null and declares queryAvailability as available status instead of missing at the end.

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@kassens has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[kassens]

You are right, thanks for the fix!

[facebook-github-bot]

@kassens has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@kassens merged this pull request in 01325ce.

[AndrewIngram]

I just lost several hours to this, is there any way to get doc fixes published?