'Hole in the graph' kind of errors. Reference (ID/SWHID) exists but object is missing.
proposed solution is a schema change
type Arc {
target: Snapshot | Release | Revision | Directory | Content
type: String! # release/revision/directory/content
swhid: SWHID!
}
type Release implements MerkleNode & Node {
id: ID!
SWHID: SWHID!
name: String
message: String
author: Person
date: DateTime
target: Arc
}