argunix: this attribute failed at evaluation time, before any build started.
attribute: packages.x86_64-linux.pykms

nix-eval-jobs error:
error:
       … while evaluating the attribute 'optionalValue.value'
         at «github:nix-community/nixpkgs.lib/f5901329dade4a6ea039af1433fb087bd9c1fe14?narHash=sha256-GOkGPcboWE9BmGCRMLX3worL4EMnsnG8MyKmXNeYuhQ%3D»/lib/modules.nix:1329:5:
         1328|
         1329|     optionalValue = if isDefined then { value = mergedValue; } else { };
             |     ^
         1330|   };

       … while evaluating a branch condition
         at «github:nix-community/nixpkgs.lib/f5901329dade4a6ea039af1433fb087bd9c1fe14?narHash=sha256-GOkGPcboWE9BmGCRMLX3worL4EMnsnG8MyKmXNeYuhQ%3D»/lib/modules.nix:1329:21:
         1328|
         1329|     optionalValue = if isDefined then { value = mergedValue; } else { };
             |                     ^
         1330|   };

       … while evaluating definitions from `/nix/store/ch5n4xdddid5859dy6c4i6lghqyx8016-source/modules/transposition.nix':

       … while evaluating definitions from `/nix/store/07imwhyzswwvc8qsbyyrnd67mwl5nm53-source/modules/packages/pykms.nix, via option perSystem':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: attribute 'unstable' missing
       at /var/lib/argunix/work/21/modules/packages/pykms.nix:3:22:
            2|   perSystem = {pkgs, ...}: {
            3|     packages.pykms = pkgs.unstable.pykms;
             |                      ^
            4|   };
       Did you mean notable?