Type of storage volume is always custom

[atrautsch]

When I print the names and types of storage volumes I always get the custom type.

pool = client.storage_pools.get(name)
volumes = pool.volumes.all()
for v in volumes:
   print(v.name, v.type)

Maybe the API changed at some point to singular instead of plural for the volume type.
For me the URLs that are used here look like this:
/1.0/storage-pools/$POOL/volumes/container/$NAME
instead of
/1.0/storage-pools/$POOL/volumes/containers/$NAME

The current swagger documentation also shows a singular type in the examples here.
My LXD version is: 4.0.8