Could not read the output of 'nix-prefetch-url' with incorrect revision

[cab404]

Update nixpkgs
  FATAL: Could not read the output of 'nix-prefetch-url'. This is a bug. Please create a
  ticket:

    https://github.com/nmattia/niv/issues/new

  Thanks! I'll buy you a beer.
  command:
  nix-prefetch-url--unpack https://github.com/NixOS/nixpkgs-channels/archive/nixos-20.09.tar.gz --name nixos-20.09.tar.gz
  stdout:

  stderr:
  error: --- FileTransferError --- nix-prefetch-url
  unable to download 'https://github.com/NixOS/nixpkgs-channels/archive/nixos-20.09.tar.gz': HTTP error 404 ('')

  response body:

  404: Not Found

  FATAL: One or more packages failed to update:
  nixpkgs: ExitFailure 1
ERROR: ExitFailure 1

Hooray, a beer! I prefer ginger!