prismlauncher: allow empty msaClientID

Upstream supports leaving the value empty, which effectively disables
the code related to that client id.

Signed-off-by: Sefa Eyeoglu <contact@scrumplex.net>

pkgs/games/prismlauncher/default.nix

@@ -11,7 +11,7 @@
 , tomlplusplus
 , ghc_filesystem
 , gamemode
-, msaClientID ? ""
+, msaClientID ? null
 , gamemodeSupport ? true
 }:
 let
@@ -42,7 +42,7 @@ stdenv.mkDerivation rec {
     tomlplusplus
   ] ++ lib.optional gamemodeSupport gamemode;
 
-  cmakeFlags = lib.optionals (msaClientID != "") [ "-DLauncher_MSA_CLIENT_ID=${msaClientID}" ]
+  cmakeFlags = lib.optionals (msaClientID != null) [ "-DLauncher_MSA_CLIENT_ID=${msaClientID}" ]
     ++ lib.optionals (lib.versionAtLeast qtbase.version "6") [ "-DLauncher_QT_VERSION_MAJOR=6" ];
 
   postUnpack = ''