Odd Error

building the system configuration...
error:
       … while calling the 'head' builtin

         at /nix/store/lf2dq57rqn8d03ybrxxi6l8gg27a4av0-source/lib/attrsets.nix:960:11:

          959|         || pred here (elemAt values 1) (head values) then
          960|           head values
             |           ^
          961|         else

       … while evaluating the attribute 'value'

         at /nix/store/lf2dq57rqn8d03ybrxxi6l8gg27a4av0-source/lib/modules.nix:809:9:

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

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

       error: attempt to call something which is not a function but a Boolean

       at /nix/store/lf2dq57rqn8d03ybrxxi6l8gg27a4av0-source/pkgs/top-level/all-packages.nix:22430:21:

        22429|   libao = callPackage ../development/libraries/libao {
        22430|     usePulseAudio = config.pulseaudio or lib.meta.availableOn stdenv.hostPlatform libpulseaudio;
             |                     ^
        22431|     inherit (darwin.apple_sdk.frameworks) CoreAudio CoreServices AudioUnit;