nixos/timezone: Fix evaluation error

Evaluation error introduced in a0d464033c2bacffa9c05d27903fb03cd09ace46.

If the value for timeZone is null it shouldn't be even tried to coerce
it into a string.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Cc: @lheckemann, @joachifm

1 files changed, 1 insertions, 1 deletions

diff --git a/nixos/modules/config/timezone.nix b/nixos/modules/config/timezone.nix
index 9f849c24c113..aa030a816d04 100644
--- a/nixos/modules/config/timezone.nix
+++ b/nixos/modules/config/timezone.nix
@@ -47,7 +47,7 @@ in
 
     environment.etc = {
       zoneinfo.source = tzdir;
-    } // lib.optionalAttrs (config.time.timeZone == null) {
+    } // lib.optionalAttrs (config.time.timeZone != null) {
         localtime.source = "/etc/zoneinfo/${config.time.timeZone}";
         localtime.mode = "direct-symlink";
       };