use mkIf for conditionals

home-manager/terminal.nix

@@ -4,13 +4,16 @@ with lib;
 {
   options.terminal = {
     nixUpdateLocation = mkOption {
-      type = types.str;
+      type = lib.types.nullOr lib.types.str;
+      default = null;
     };
     flakeUpdateLocation = mkOption {
-      type = types.str;
+      type = lib.types.nullOr lib.types.str;
+      default = null;
     };
     homeUpdateLocation = mkOption {
-      type = types.str;
+      type = lib.types.nullOr lib.types.str;
+      default = null;
     };
   };
 
@@ -139,18 +142,38 @@ with lib;
 
       topgrade = with config.terminal;{
         enable = true;
-        settings = {
+        # settings = {
+        #   misc = {
+        #     assume_yes = true;
+        #   };
+        #   linux = {
+        #     nix_arguments = if nixUpdateLocation != null then "--flake ${nixUpdateLocation}" else default;
+        #     home_manager_arguments = if homeUpdateLocation != null then "--flake ${homeUpdateLocation}" else "";
+        #   };
+        #   pre_commands = {
+        #     nix-flake-update = if flakeUpdateLocation != null then "sudo nix flake update --flake ${flakeUpdateLocation}" else "";
+        #   };
+        # };
+        settings = mkMerge [{
           misc = {
             assume_yes = true;
           };
+        }
+          (mkIf (nixUpdateLocation != null) {
             linux = {
-            nix_arguments = if nixUpdateLocation then "--flake ${nixUpdateLocation}" else null;
+              nix_arguments = "--flake ${nixUpdateLocation}";
-            home_manager_arguments = if homeUpdateLocation then "--flake ${homeUpdateLocation}" else null;
             };
+          })
+          (mkIf (homeUpdateLocation != null) {
+            linux = {
+              home_manager_arguments = "--flake ${homeUpdateLocation}";
+            };
+          })
+          (mkIf (flakeUpdateLocation != null) {
             pre_commands = {
-            nix-flake-update = if flakeUpdateLocation then "sudo nix flake update --flake ${flakeUpdateLocation}" else null;
+              nix-flake-update = "sudo nix flake update --flake ${flakeUpdateLocation}";
-          };
             };
+          })];
       };
 
       alacritty = {