nixos/vaultwarden: Allow multiple environment files

Change type of `environmentFile` to also allow passing a list of paths
in order to have multiple environment files.

nixos/modules/services/security/vaultwarden/default.nix

@@ -172,11 +172,11 @@ in
     };
 
     environmentFile = lib.mkOption {
-      type = with lib.types; nullOr path;
-      default = null;
+      type = with lib.types; coercedTo path lib.singleton (listOf path);
+      default = [ ];
       example = "/var/lib/vaultwarden.env";
       description = ''
-        Additional environment file as defined in {manpage}`systemd.exec(5)`.
+        Additional environment file or files as defined in {manpage}`systemd.exec(5)`.
 
         Secrets like {env}`ADMIN_TOKEN` and {env}`SMTP_PASSWORD`
         should be passed to the service without adding them to the world-readable Nix store.
@@ -225,7 +225,7 @@ in
       serviceConfig = {
         User = user;
         Group = group;
-        EnvironmentFile = [ configFile ] ++ lib.optional (cfg.environmentFile != null) cfg.environmentFile;
+        EnvironmentFile = [ configFile ] ++ cfg.environmentFile;
         ExecStart = lib.getExe vaultwarden;
         LimitNOFILE = "1048576";
         CapabilityBoundingSet = [ "" ];