executeFields (for queries) returns MaybePromise
executeFieldsSerially (for mutations) returns Promise and this is not "sync"

https://github.com/graphql/graphql-js/blob/master/src/execution/execute.js#L399

Could you please rewrite executeFieldsSerially to return MaybePromise also?

Thanks! :)