Merge branch 'fix/nix-fpm-env'

nix/nixos-module.nix

@@ -46,7 +46,11 @@ let
     SESSION_SECURE_COOKIE = lib.boolToString cfg.backend.cookieSecure;
   };
 
-  fpmEnvironment = appEnvironment // {
+  fpmBaseEnvironment = lib.filterAttrs (
+    environmentName: environmentValue: environmentValue != ""
+  ) appEnvironment;
+
+  fpmEnvironment = fpmBaseEnvironment // {
     APP_KEY = "$APP_KEY";
   };