[TestFixture]
public class MongoCases_Linq3_ProjectWithNullableGuid
{
    [Test]
    public async Task Test()
    {
        BsonSerializer.TryRegisterSerializer(new GuidSerializer(GuidRepresentation.CSharpLegacy));

        var mongoClientSettings = MongoClientSettings.FromConnectionString("mongodb://localhost:27017");

        var mongoClient = new MongoClient(mongoClientSettings);

        var db = mongoClient.GetDatabase(Guid.NewGuid().ToString()[..8]);

        var collection = db.GetCollection<User>("users");

        var user = new User
        {
            Tasks =
            [
                new UserTask
                {
                    Summary = "Task 1",
                    CustomerId = null
                }
            ]
        };

        await collection.InsertOneAsync(user);

        var query = collection
            .Find(Builders<User>.Filter.Empty)
            .Project(u => u.Tasks
                .Where(t => t.CustomerId.HasValue)
                .Select(t => t.CustomerId!.Value)
            );

        var customerIds = (await query.FirstOrDefaultAsync()).ToArray();

        // System.FormatException : Cannot deserialize a 'Guid' from BsonType 'Null'.
        //     at MongoDB.Bson.Serialization.Serializers.GuidSerializer.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
        //     at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer`1 serializer, BsonDeserializationContext context)
        //     at MongoDB.Driver.Linq.Linq3Implementation.Serializers.IEnumerableSerializerBase`2.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
        //     at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer`1 serializer, BsonDeserializationContext context)
        //     at MongoDB.Driver.Linq.Linq3Implementation.Serializers.WrappedValueSerializer`1.Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
        //     at MongoDB.Bson.Serialization.IBsonSerializerExtensions.Deserialize[TValue](IBsonSerializer`1 serializer, BsonDeserializationContext context)
        //     at MongoDB.Driver.Core.Operations.CursorBatchDeserializationHelper.DeserializeBatch[TDocument](RawBsonArray batch, IBsonSerializer`1 documentSerializer, MessageEncoderSettings messageEncoderSettings)
        //     at MongoDB.Driver.Core.Operations.FindOperation`1.CreateFirstCursorBatch(BsonDocument cursorDocument)
        //     at MongoDB.Driver.Core.Operations.FindOperation`1.CreateCursor(IChannelSourceHandle channelSource, IChannelHandle channel, BsonDocument commandResult)
        //     at MongoDB.Driver.Core.Operations.FindOperation`1.ExecuteAsync(OperationContext operationContext, RetryableReadContext context)
        //     at MongoDB.Driver.Core.Operations.FindOperation`1.ExecuteAsync(OperationContext operationContext, IReadBinding binding)
        //     at MongoDB.Driver.OperationExecutor.ExecuteReadOperationAsync[TResult](OperationContext operationContext, IClientSessionHandle session, IReadOperation`1 operation, ReadPreference readPreference, Boolean allowChannelPinning)
        //     at MongoDB.Driver.MongoCollectionImpl`1.ExecuteReadOperationAsync[TResult](IClientSessionHandle session, IReadOperation`1 operation, ReadPreference explicitReadPreference, Nullable`1 timeout, CancellationToken cancellationToken)
        //     at MongoDB.Driver.MongoCollectionImpl`1.FindAsync[TProjection](FilterDefinition`1 filter, FindOptions`2 options, CancellationToken cancellationToken)
        //     at MongoDB.Driver.IAsyncCursorSourceExtensions.FirstOrDefaultAsync[TDocument](IAsyncCursorSource`1 source, CancellationToken cancellationToken)

        Assert.That(customerIds.Length, Is.EqualTo(0));
    }

    class User
    {
        [BsonId]
        public Guid Id { get; set; }

        [BsonElement("tasks")]
        public IReadOnlyCollection<UserTask> Tasks { get; set; }
    }

    class UserTask
    {
        [BsonElement("summary")]
        public string Summary { get; set; }

        [BsonElement("customerId"), BsonIgnoreIfNull]
        public Guid? CustomerId { get; set; }
    }
}