Arvados

When requesting an collection json with `arv get`, an empty "unsigned_manifest_text" field is always returned, e.g.:

$ arv get ce8i5-4zz18-k74yj38bjtguqg4
{
 "created_at":"2020-08-19T16:55:59.402173000Z",
 "current_version_uuid":"ce8i5-4zz18-k74yj38bjtguqg4",
 "delete_at":null,
 "description":null,
 "etag":"xwcle1rl4myjdky8w0h3p2vy",
 "file_count":1,
 "file_size_total":0,
 "is_trashed":false,
 "kind":"arvados#collection",
 "manifest_text":". d41d8cd98f00b204e9800998ecf8427e+0+A737446d9e44ec6b2ec5554bf88f9ad35dd986053@6126792a 0:0:file1.txt\n",
 "modified_at":"2020-08-19T16:55:59.394989000Z",
 "modified_by_client_uuid":"ce8i5-ozdt8-g1uv539034n3e95",
 "modified_by_user_uuid":"ce8i5-tpzed-xo2k4i24bjzwedw",
 "name":"My collection",
 "owner_uuid":"ce8i5-j7d0g-od6aji7qdjn6yux",
 "portable_data_hash":"166d3c4d1b5bc5484abd77e46b69f890+51",
 "preserve_version":false,
 "properties":{},
 "replication_confirmed":0,
 "replication_confirmed_at":"2021-07-28T19:11:15.331522000Z",
 "replication_desired":null,
 "storage_classes_confirmed":[
  "default" 
 ],
 "storage_classes_confirmed_at":"2021-07-28T19:11:15.331522000Z",
 "storage_classes_desired":[
  "default" 
 ],
 "trash_at":null,
 "unsigned_manifest_text":"",
 "uuid":"ce8i5-4zz18-k74yj38bjtguqg4",
 "version":1
}

This also happens on our latest release (2.2.1).

Controller is supposed to strip that empty field; it is only supposed to be in the output (and populated) when it is explicitly requested.