lib/modules: skip optional + ++ in evalOptionValue when no default (#510028)

    let

      # Add in the default value for this option, if any.

      defs' =

        (optional (opt ? default) {

        if opt ? default then

          [

            {

              file = head opt.declarations;

              value = mkOptionDefault opt.default;

        })

        ++ defs;

            }

          ]

          ++ defs

        else

          defs;

      # Handle properties, check types, and merge everything together.

      res =