fixed lidarr null albums wiping cf entries

code/backend/Cleanuparr.Infrastructure.Tests/Features/Arr/LidarrClientTests.cs

@@ -459,11 +459,21 @@ public class LidarrClientTests
     }
 
     [Fact]
-    public async Task GetAlbumsAsync_NullBody_ReturnsEmpty()
+    public async Task GetAlbumsAsync_NullBody_Throws()
     {
         // Arrange
         _httpMessageHandler.SetupResponse((_, _) => Task.FromResult(JsonNullResponse()));
 
+        // Act & Assert
+        await Should.ThrowAsync<InvalidOperationException>(() => _client.GetAlbumsAsync(_arrInstance, 7));
+    }
+
+    [Fact]
+    public async Task GetAlbumsAsync_EmptyArray_ReturnsEmpty()
+    {
+        // Arrange
+        _httpMessageHandler.SetupResponse((_, _) => Task.FromResult(RawJsonResponse("[]")));
+
         // Act
         List<SearchableAlbum> albums = await _client.GetAlbumsAsync(_arrInstance, 7);
 

code/backend/Cleanuparr.Infrastructure/Features/Arr/LidarrClient.cs

@@ -226,7 +226,9 @@ public class LidarrClient : ArrClient, ILidarrClient
         using HttpResponseMessage response = await _httpClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
         response.EnsureSuccessStatusCode();
 
-        return await DeserializeStreamAsync<List<SearchableAlbum>>(response, cancellationToken) ?? [];
+        // An empty list would make the CF syncer delete every album entry of the artist
+        return await DeserializeStreamAsync<List<SearchableAlbum>>(response, cancellationToken)
+            ?? throw new InvalidOperationException($"Lidarr returned null albums for artist {artistId}");
     }
 
     public async Task<List<ArrTrackFile>> GetTrackFilesAsync(ArrInstance arrInstance, long artistId, CancellationToken cancellationToken = default)