corenix: allow setting extraFiles.*.src to null

modules/corenix/default.nix

@@ -7,7 +7,7 @@ let
 
   fileOptions.options = {
     src = mkOption {
-      type = types.path;
+      type = types.nullOr types.path;
     };
 
     type = mkOption {
@@ -38,7 +38,7 @@ in {
 
   config = {
     corenix.installCommands = let
-      filteredFiles = filterAttrs (k: v: v != null) cfg.extraFiles;
+      filteredFiles = filterAttrs (k: v: v.src != null) cfg.extraFiles;
       filesList = mapAttrsToList (k: v: v // { name = k; }) filteredFiles;
     in concatMapStringsSep "\n" (file: 
       if file.type == "payload" then ''