[ads] Fixes crash when migrating the legacy confirmation queue

components/brave_ads/core/internal/legacy_migration/confirmations/legacy_confirmation_migration.cc

@@ -46,7 +46,7 @@ void MigrateConfirmationState(InitializeCallback callback) {
            [](InitializeCallback callback,
               const std::optional<std::string>& json) {
              if (!json) {
-               // Confirmation state does not exist
+               // Confirmation state does not exist.
                return SuccessfullyMigrated(std::move(callback));
              }
 
@@ -63,7 +63,11 @@ void MigrateConfirmationState(InitializeCallback callback) {
 
              const absl::optional<ConfirmationList> confirmations =
                  json::reader::ReadConfirmations(*json);
-             CHECK(confirmations);
+             if (!confirmations) {
+               // Confirmation queue state does not exist.
+               return SuccessfullyMigrated(std::move(callback));
+             }
+
              ConfirmationQueueItemList confirmation_queue_items;
              for (const auto& confirmation : *confirmations) {
                const ConfirmationQueueItemInfo confirmation_queue_item =

components/brave_ads/core/internal/legacy_migration/confirmations/legacy_confirmation_migration_confirmations_json_reader_util.cc

@@ -136,6 +136,8 @@ std::optional<ConfirmationInfo> ParseConfirmation(
   // User data
   if (const auto* const value = dict.FindDict(kConfirmationUserDataKey)) {
     confirmation.user_data.fixed = value->Clone();
+  } else {
+    return std::nullopt;
   }
 
   // Reward