fix: Handle unknown item types gracefully in DeserializeBaseItem

When querying items with recursive=true, items with types from removed
plugins would cause a 500 error. Now these items are skipped with a
warning log instead of throwing an exception.

Fixes #15945

3 files changed, 100 insertions, 19 deletions

diff --git a/Jellyfin.Server.Implementations/Item/BaseItemRepository.cs b/Jellyfin.Server.Implementations/Item/BaseItemRepository.cs
index 85ab00a2b..b7f1c23e0 100644
--- a/Jellyfin.Server.Implementations/Item/BaseItemRepository.cs
+++ b/Jellyfin.Server.Implementations/Item/BaseItemRepository.cs
@@ -277,7 +277,7 @@ public sealed class BaseItemRepository
         dbQuery = ApplyQueryPaging(dbQuery, filter);
         dbQuery = ApplyNavigations(dbQuery, filter);
 
-        result.Items = dbQuery.AsEnumerable().Where(e => e is not null).Select(w => DeserializeBaseItem(w, filter.SkipDeserialization)).ToArray();
+        result.Items = dbQuery.AsEnumerable().Where(e => e is not null).Select(w => DeserializeBaseItem(w, filter.SkipDeserialization)).Where(dto => dto is not null).ToArray()!;
         result.StartIndex = filter.StartIndex ?? 0;
         return result;
     }
@@ -297,7 +297,7 @@ public sealed class BaseItemRepository
         dbQuery = ApplyQueryPaging(dbQuery, filter);
         dbQuery = ApplyNavigations(dbQuery, filter);
 
-        return dbQuery.AsEnumerable().Where(e => e is not null).Select(w => DeserializeBaseItem(w, filter.SkipDeserialization)).ToArray();
+        return dbQuery.AsEnumerable().Where(e => e is not null).Select(w => DeserializeBaseItem(w, filter.SkipDeserialization)).Where(dto => dto is not null).ToArray()!;
     }
 
     /// <inheritdoc/>
@@ -341,7 +341,7 @@ public sealed class BaseItemRepository
 
         mainquery = ApplyNavigations(mainquery, filter);
 
-        return mainquery.AsEnumerable().Where(e => e is not null).Select(w => DeserializeBaseItem(w, filter.SkipDeserialization)).ToArray();
+        return mainquery.AsEnumerable().Where(e => e is not null).Select(w => DeserializeBaseItem(w, filter.SkipDeserialization)).Where(dto => dto is not null).ToArray()!;
     }
 
     /// <inheritdoc />
@@ -1159,7 +1159,7 @@ public sealed class BaseItemRepository
         return type.GetCustomAttribute<RequiresSourceSerialisationAttribute>() == null;
     }
 
-    private BaseItemDto DeserializeBaseItem(BaseItemEntity baseItemEntity, bool skipDeserialization = false)
+    private BaseItemDto? DeserializeBaseItem(BaseItemEntity baseItemEntity, bool skipDeserialization = false)
     {
         ArgumentNullException.ThrowIfNull(baseItemEntity, nameof(baseItemEntity));
         if (_serverConfigurationManager?.Configuration is null)
@@ -1182,11 +1182,19 @@ public sealed class BaseItemRepository
     /// <param name="logger">Logger.</param>
     /// <param name="appHost">The application server Host.</param>
     /// <param name="skipDeserialization">If only mapping should be processed.</param>
-    /// <returns>A mapped BaseItem.</returns>
-    /// <exception cref="InvalidOperationException">Will be thrown if an invalid serialisation is requested.</exception>
-    public static BaseItemDto DeserializeBaseItem(BaseItemEntity baseItemEntity, ILogger logger, IServerApplicationHost? appHost, bool skipDeserialization = false)
+    /// <returns>A mapped BaseItem, or null if the item type is unknown.</returns>
+    public static BaseItemDto? DeserializeBaseItem(BaseItemEntity baseItemEntity, ILogger logger, IServerApplicationHost? appHost, bool skipDeserialization = false)
     {
-        var type = GetType(baseItemEntity.Type) ?? throw new InvalidOperationException("Cannot deserialize unknown type.");
+        var type = GetType(baseItemEntity.Type);
+        if (type is null)
+        {
+            logger.LogWarning(
+                "Skipping item {ItemId} with unknown type '{ItemType}'. This may indicate a removed plugin or database corruption.",
+                baseItemEntity.Id,
+                baseItemEntity.Type);
+            return null;
+        }
+
         BaseItemDto? dto = null;
         if (TypeRequiresDeserialization(type) && baseItemEntity.Data is not null && !skipDeserialization)
         {
@@ -1353,10 +1361,9 @@ public sealed class BaseItemRepository
                 .. resultQuery
                     .AsEnumerable()
                     .Where(e => e is not null)
-                    .Select(e =>
-                    {
-                        return (DeserializeBaseItem(e.item, filter.SkipDeserialization), e.itemCount);
-                    })
+                    .Select(e => (Item: DeserializeBaseItem(e.item, filter.SkipDeserialization), e.itemCount))
+                    .Where(e => e.Item is not null)
+                    .Select(e => (e.Item!, e.itemCount))
             ];
         }
         else
@@ -1367,10 +1374,9 @@ public sealed class BaseItemRepository
                 .. query
                     .AsEnumerable()
                     .Where(e => e is not null)
-                    .Select<BaseItemEntity, (BaseItemDto, ItemCounts?)>(e =>
-                    {
-                        return (DeserializeBaseItem(e, filter.SkipDeserialization), null);
-                    })
+                    .Select(e => (Item: DeserializeBaseItem(e, filter.SkipDeserialization), ItemCounts: (ItemCounts?)null))
+                    .Where(e => e.Item is not null)
+                    .Select(e => (e.Item!, e.ItemCounts))
             ];
         }
 
@@ -2671,6 +2677,6 @@ public sealed class BaseItemRepository
             .Where(e => artistNames.Contains(e.Name))
             .ToArray();
 
-        return artists.GroupBy(e => e.Name).ToDictionary(e => e.Key!, e => e.Select(f => DeserializeBaseItem(f)).Cast<MusicArtist>().ToArray());
+        return artists.GroupBy(e => e.Name).ToDictionary(e => e.Key!, e => e.Select(f => DeserializeBaseItem(f)).Where(dto => dto is not null).Cast<MusicArtist>().ToArray());
     }
 }
diff --git a/Jellyfin.Server/Migrations/Routines/MigrateLibraryDb.cs b/Jellyfin.Server/Migrations/Routines/MigrateLibraryDb.cs
index d221d1853..4b1e53a35 100644
--- a/Jellyfin.Server/Migrations/Routines/MigrateLibraryDb.cs
+++ b/Jellyfin.Server/Migrations/Routines/MigrateLibraryDb.cs
@@ -1247,8 +1247,11 @@ internal class MigrateLibraryDb : IDatabaseMigrationRoutine
         }
 
         var baseItem = BaseItemRepository.DeserializeBaseItem(entity, _logger, null, false);
-        var dataKeys = baseItem.GetUserDataKeys();
-        userDataKeys.AddRange(dataKeys);
+        if (baseItem is not null)
+        {
+            var dataKeys = baseItem.GetUserDataKeys();
+            userDataKeys.AddRange(dataKeys);
+        }
 
         return (entity, userDataKeys.ToArray());
     }
diff --git a/tests/Jellyfin.Server.Implementations.Tests/Item/BaseItemRepositoryTests.cs b/tests/Jellyfin.Server.Implementations.Tests/Item/BaseItemRepositoryTests.cs
new file mode 100644
index 000000000..c450cbb0e
--- /dev/null
+++ b/tests/Jellyfin.Server.Implementations.Tests/Item/BaseItemRepositoryTests.cs
@@ -0,0 +1,72 @@
+using System;
+using Jellyfin.Database.Implementations.Entities;
+using Jellyfin.Server.Implementations.Item;
+using MediaBrowser.Controller;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Moq;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Item;
+
+public class BaseItemRepositoryTests
+{
+    [Fact]
+    public void DeserializeBaseItem_WithUnknownType_ReturnsNull()
+    {
+        // Arrange
+        var entity = new BaseItemEntity
+        {
+            Id = Guid.NewGuid(),
+            Type = "NonExistent.Plugin.CustomItemType"
+        };
+
+        // Act
+        var result = BaseItemRepository.DeserializeBaseItem(entity, NullLogger.Instance, null, false);
+
+        // Assert
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void DeserializeBaseItem_WithUnknownType_LogsWarning()
+    {
+        // Arrange
+        var entity = new BaseItemEntity
+        {
+            Id = Guid.NewGuid(),
+            Type = "NonExistent.Plugin.CustomItemType"
+        };
+        var loggerMock = new Mock<ILogger>();
+
+        // Act
+        BaseItemRepository.DeserializeBaseItem(entity, loggerMock.Object, null, false);
+
+        // Assert
+        loggerMock.Verify(
+            x => x.Log(
+                LogLevel.Warning,
+                It.IsAny<EventId>(),
+                It.Is<It.IsAnyType>((v, t) => v.ToString()!.Contains("unknown type", StringComparison.OrdinalIgnoreCase)),
+                It.IsAny<Exception?>(),
+                It.IsAny<Func<It.IsAnyType, Exception?, string>>()),
+            Times.Once);
+    }
+
+    [Fact]
+    public void DeserializeBaseItem_WithKnownType_ReturnsItem()
+    {
+        // Arrange
+        var entity = new BaseItemEntity
+        {
+            Id = Guid.NewGuid(),
+            Type = "MediaBrowser.Controller.Entities.Movies.Movie"
+        };
+
+        // Act
+        var result = BaseItemRepository.DeserializeBaseItem(entity, NullLogger.Instance, null, false);
+
+        // Assert
+        Assert.NotNull(result);
+    }
+}