less: generate lesskey only when non-empty

modules/programs/less.nix

@@ -34,6 +34,6 @@ in
   config = lib.mkIf cfg.enable {
     home.packages = lib.mkIf (cfg.package != null) [ cfg.package ];
 
-    xdg.configFile."lesskey".text = cfg.keys;
+    xdg.configFile."lesskey" = lib.mkIf (cfg.keys != "") { text = cfg.keys; };
   };
 }

tests/modules/programs/less/default.nix

@@ -1 +1,4 @@
-{ less-with-custom-keys = ./less-with-custom-keys.nix; }
+{
+  less-custom-keys = ./custom-keys.nix;
+  less-no-keys = ./no-keys.nix;
+}

tests/modules/programs/less/no-keys.nix

@@ -0,0 +1,7 @@
+{
+  programs.less.enable = true;
+
+  nmt.script = ''
+    assertPathNotExists home-files/.config/lesskey
+  '';
+}