generate-node-key does not work in docker

Command:
docker run parity/subkey:2.0.0-rc6 generate-node-key --file ~/node-key

Expected Result:
A file named node-key being created in $USER's home directory.
OR
If it cannot be saved to a file (because docker?), output the following:

{
    "secretPeerKey": "<KEY>",
    "peerId": "<PEER_ID>"
}

Actual Result:
Error: Io(Os { code: 2, kind: NotFound, message: "No such file or directory" })
OR
when used without the --file option

subkey-generate-node-key 2.0.0-rc6
Generate a random node libp2p key, save it to file and print its peer ID

USAGE:
    subkey generate-node-key --file <file>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information