nixos/parsedmarc: Fix smtp.to and default elasticsearch url

Previously evaluaton would fail if `smtp.to` was not set, since the
default case was not handled.

With the current versions of the python elasticsearch libraries, any
configuration containing the modules default would fail since it's not a
valid URL.

The issue adressed in #279068 is also adressed, thuse closes #279068.

nixos/modules/services/monitoring/parsedmarc.nix

@@ -301,7 +301,7 @@ in
               description = ''
                 The addresses to send outgoing mail to.
               '';
-              apply = x: if x == [] then null else lib.concatStringsSep "," x;
+              apply = x: if x == [] || x == null then null else lib.concatStringsSep "," x;
             };
           };
 
@@ -446,7 +446,7 @@ in
     services.parsedmarc.settings = lib.mkMerge [
       (lib.mkIf cfg.provision.elasticsearch {
         elasticsearch = {
-          hosts = [ "localhost:9200" ];
+          hosts = [ "http://localhost:9200" ];
           ssl = false;
         };
       })