Remove uses of the "merge" option attribute

It's redundant because you can (and should) specify an option type, or
an apply function.

1 files changed, 1 insertions, 1 deletions

diff --git a/nixos/modules/system/activation/top-level.nix b/nixos/modules/system/activation/top-level.nix
index a04914bedaf7..7b1c7d611d35 100644
--- a/nixos/modules/system/activation/top-level.nix
+++ b/nixos/modules/system/activation/top-level.nix
@@ -172,9 +172,9 @@ in
     };
 
     system.extraSystemBuilderCmds = mkOption {
+      type = types.lines;
       internal = true;
       default = "";
-      merge = concatStringsSep "\n";
       description = ''
         This code will be added to the builder creating the system store path.
       '';