execute: Forbid to return null from serialize function

[IvanGoncharov]

Fixes #1579

[yaacovCR]

@IvanGoncharov I know a while back, but doesn’t this change (as opposed to #1579) raise field errors for null leaf values even when the types are nullable?

spec reference: first sentence here https://spec.graphql.org/draft/#sec-Non-Null.Result-Coercion

[IvanGoncharov]

@yaacovCR It's forbidden by the spec here:
https://spec.graphql.org/draft/#sel-IANRLHHCDCECCGgB2xE

[IvanGoncharov]

@yaacovCR Null is separate from scalars, they are not converted to/from scalars.
Because it would cause them to not be reversable.

[yaacovCR]

Thanks for quick response!

Ah, a reminder that nullable means that null is allowed/valid in response (does not cause error to bubble up), not that it’s actually not an error, which it sometimes isn’t (composite types) and sometimes is (for leaf values).

Makes sense in intent and practice now, appreciated!

[yaacovCR]

I guess the error message should be “non-null” value not “non-nullable”.

[IvanGoncharov]

I guess the error message should be “non-null” value not “non-nullable”.

@yaacovCR It also includes undefined since it is nullable in JS (undefined == null).

[yaacovCR]

I still think that’s a bit wrong grammar wise.

Undefined is not “nullable” . It’s not anything able, it’s just a set value, we could say the return value of serialize is not nullable if the parameter is not null, so it can’t return x value, but we can’t say the expected return value itself is a non nullable value.

anyway it’s splitting hairs, thanks for explaining!!!!