Error after updating flakes

Hi people,

I have updated yesterday my flakes to the most recent unstable version and with that, I started getting an error.

       … while calling the 'head' builtin

         at /nix/store/g68f5abh3xhcz8xsdlfw7wkgkkcx3nwy-source/lib/attrsets.nix:820:11:

          819|         || pred here (elemAt values 1) (head values) then
          820|           head values
             |           ^
          821|         else

       … while evaluating the attribute 'value'

         at /nix/store/g68f5abh3xhcz8xsdlfw7wkgkkcx3nwy-source/lib/modules.nix:807:9:

          806|     in warnDeprecation opt //
          807|       { value = builtins.addErrorContext "while evaluating the option `${showOption loc}':" value;
             |         ^
          808|         inherit (res.defsFinal') highestPrio;

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

       Failed assertions:
       - Your system configures nixpkgs with an externally created instance.
       `nixpkgs.config` options should be passed when creating the instance instead.

I saw a similar thing on another topic, but the person there was using snowfall to define their flake file.

Does anyone know what I can do to get around this issue? Thanks.

Well, I tried almost everything during these last 3 days, everything but this :man_facepalming:

I was using a nixpkgs.config.allowUnfree = true;, but was already settings the allowUnfree on the flake file. With the new check that was introduced, it validates this duplication.