Without the change the eval fails as:

    $ nix build --no-link -f. pkgsStatic.botan3
    error:
       … while calling a functor (an attribute set with a '__functor' attribute)
         at lib/customisation.nix:317:7:
          316|     if missingArgs == { } then
          317|       makeOverridable f allArgs
             |       ^
          318|     # This needs to be an abort so it can't be caught with `builtins.tryEval`,

       … while evaluating a branch condition
         at lib/customisation.nix:182:7:
          181|       in
          182|       if isAttrs result then
             |       ^
          183|         result

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

       error: attribute 'libxccStdenv' missing
       at pkgs/by-name/bo/botan3/package.nix:37:28:
           36| let
           37|   stdenv' = if static then buildPackages.libxccStdenv else stdenv;
             |                            ^
           38| in