Better handling of missing channels

[cnrdh]

Example with missing:
https://pubs.deno.dev/nva/01907a836669-1d67d7b2-33c8-4817-baa9-466be9d11b18

[cnrdh]

"reference": {
"type": "Reference",
"publicationContext": {
"type": "Report",
"series": {
"type": "Series",
"id": "https://api.test.nva.aws.unit.no/publication-channels-v2/series/FB04218E-1FC6-4042-9733-D34BB47050F6/2021"
},
"seriesNumber": "Issue:058",
"publisher": {
"type": "UnconfirmedPublisher",
"name": "Norwegian Polar Institute",
"valid": true
},
"isbnList": [
"9788276664454"
],
"additionalIdentifiers": []
},
"publicationInstance": {
"type": "ReportResearch",
"pages": {
"type": "MonographPages",
"pages": "56",
"illustrated": false
}
}
}