Describe the bug

It seems that nix upgrade-nix is incompatible with nix profile.

Steps To Reproduce

1. Install a package with nix profile install nixpkgs#hello
2. Try to upgrade nix with nix upgrade-nix. The following error is displayed:

nix upgrade-nix 
error: directory '/Users/smaret/.nix-profile/bin' does not appear to be part of a Nix profile

Expected behavior

nix upgrade-nix should upgrade to the latest stable release

nix-env --version output

nix-env --version
nix-env (Nix) 2.4

Additional information

Relevant line in nix source code: