* we should look for both embedded relationship and relationship key,
so in cases like for commit, when there's a full commit data on
"commit" property, and only id at "commit_id", we will use commit data
* we can't add @type to V2 fallback, because in other places we chack
for @type to distinguish V2 and V3 payloads
* there's no need to include a record in "included" if there's only a
type and an id there
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