fix- json syntax exceptions

app/src/main/java/it/niedermann/owncloud/notes/persistence/CapabilitiesClient.java

@@ -13,16 +13,10 @@
 import androidx.annotation.Nullable;
 import androidx.annotation.WorkerThread;
 
-import com.nextcloud.android.sso.api.ParsedResponse;
 import com.nextcloud.android.sso.model.SingleSignOnAccount;
 
-import java.util.Map;
-
-import it.niedermann.owncloud.notes.persistence.sync.OcsAPI;
 import it.niedermann.owncloud.notes.shared.model.Capabilities;
-import it.niedermann.owncloud.notes.shared.model.OcsResponse;
-import it.niedermann.owncloud.notes.shared.model.OcsUser;
-import retrofit2.Response;
+import it.niedermann.owncloud.notes.util.ThrowableExtensionsKt;
 
 @WorkerThread
 public class CapabilitiesClient {
@@ -34,6 +28,8 @@ public class CapabilitiesClient {
     @WorkerThread
     public static Capabilities getCapabilities(@NonNull Context context, @NonNull SingleSignOnAccount ssoAccount, @Nullable String lastETag, @NonNull ApiProvider apiProvider) throws Throwable {
         final var ocsAPI = apiProvider.getOcsAPI(context, ssoAccount);
+        final var repository = NotesRepository.getInstance(context);
+
         try {
             final var response = ocsAPI.getCapabilities(lastETag).blockingSingle();
             final var capabilities = response.getResponse().ocs.data;
@@ -44,16 +40,20 @@ public static Capabilities getCapabilities(@NonNull Context context, @NonNull Si
                 Log.w(TAG, "Response headers of capabilities are null");
             }
 
-            final var repository = NotesRepository.getInstance(context);
             repository.insertCapabilities(capabilities);
 
             return capabilities;
-        } catch (RuntimeException e) {
-            final var cause = e.getCause();
+        } catch (Throwable t) {
+            if (ThrowableExtensionsKt.isEmptyResponseCast(t)) {
+                Log.d(TAG, "Server returned empty response - Notes not modified.");
+                return repository.getCapabilities();
+            }
+
+            final var cause = t.getCause();
             if (cause != null) {
                 throw cause;
             } else {
-                throw e;
+                throw t;
             }
         }
     }

app/src/main/java/it/niedermann/owncloud/notes/persistence/NotesServerSyncTask.java

@@ -42,6 +42,7 @@
 import it.niedermann.owncloud.notes.shared.model.ISyncCallback;
 import it.niedermann.owncloud.notes.shared.model.SyncResultStatus;
 import it.niedermann.owncloud.notes.shared.util.ApiVersionUtil;
+import it.niedermann.owncloud.notes.util.ThrowableExtensionsKt;
 
 
 /**
@@ -280,6 +281,11 @@ private boolean pullRemoteChanges() {
             return true;
         } catch (Throwable t) {
             final Throwable cause = t.getCause();
+            if (ThrowableExtensionsKt.isEmptyResponseCast(t)) {
+                Log.d(TAG, "Server returned empty response - Notes not modified.");
+                return true;
+            }
+
             if (t.getClass() == RuntimeException.class && cause != null) {
                 if (cause.getClass() == NextcloudHttpRequestFailedException.class || cause instanceof NextcloudHttpRequestFailedException) {
                     final NextcloudHttpRequestFailedException httpException = (NextcloudHttpRequestFailedException) cause;

app/src/main/java/it/niedermann/owncloud/notes/util/ThrowableExtensions.kt

@@ -0,0 +1,27 @@
+/*
+ * Nextcloud Notes - Android Client
+ *
+ * SPDX-FileCopyrightText: 2021-2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+package it.niedermann.owncloud.notes.util
+
+import com.nextcloud.android.sso.api.EmptyResponse
+
+/**
+ * Extension function to detect a specific ClassCastException caused by an empty API response.
+ *
+ * This is used to identify cases where the API returns an empty response body,
+ * which leads to a `ClassCastException` when attempting to deserialize it into a non-nullable type.
+ *
+ * In particular, when the API processes an empty Reader (e.g., no changes detected),
+ * it may result in a `JsonSyntaxException` or similar parsing error.
+ * This function helps to safely ignore such cases by checking if the exception
+ * is a `ClassCastException` involving the `EmptyResponse` class.
+ *
+ * @return `true` if the Throwable is a ClassCastException referencing `EmptyResponse`, otherwise `false`.
+ */
+fun Throwable.isEmptyResponseCast(): Boolean {
+    return this is ClassCastException &&
+            (message?.contains(EmptyResponse::class.simpleName ?: "") == true)
+}