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CSHARP-6043: NullReferenceException in IEnumerableSerializerBase.Serialize when projecting nullable array with conditional Select #2012

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Merged
papafe merged 2 commits into from
May 27, 2026
Merged

CSHARP-6043: NullReferenceException in IEnumerableSerializerBase.Serialize when projecting nullable array with conditional Select #2012

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1196d94
CSHARP-6043: NullReferenceException in IEnumerableSerializerBase.Seri…
papafe May 26, 2026
d9415bc
Removed test.
papafe May 26, 2026
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11 changes: 11 additions & 0 deletions src/MongoDB.Driver/Linq/Linq3Implementation/Serializers/IEnumerableSerializerBase.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
*/

using System.Collections.Generic;
using MongoDB.Bson;
using MongoDB.Bson.Serialization;
using MongoDB.Bson.Serialization.Serializers;
using MongoDB.Driver.Core.Misc;
Expand All @@ -36,6 +37,11 @@ public IEnumerableSerializerBase(IBsonSerializer<TItem> itemSerializer)
public override TEnumerable Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
{
var reader = context.Reader;
if (reader.GetCurrentBsonType() == BsonType.Null)
{
reader.ReadNull();
return default;
}
reader.ReadStartArray();
var items = new List<TItem>();
while (reader.ReadBsonType() != 0)
Expand Down Expand Up @@ -64,6 +70,11 @@ obj is IEnumerableSerializerBase<TEnumerable, TItem> other &&
public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, TEnumerable value)
{
var writer = context.Writer;
if (value == null)
{
writer.WriteNull();
return;
}
Comment on lines 70 to +77
writer.WriteStartArray();
foreach (var item in value)
{
Expand Down
32 changes: 32 additions & 0 deletions ...ngoDB.Driver.Tests/Linq/Linq3Implementation/Serializers/IEnumerableSerializerBaseTests.cs
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Expand Up @@ -16,6 +16,7 @@
using System.Collections.Generic;
using FluentAssertions;
using MongoDB.Bson;
using MongoDB.Bson.IO;
using MongoDB.Bson.Serialization;
using MongoDB.Bson.Serialization.Serializers;
using MongoDB.Driver.Linq.Linq3Implementation.Serializers;
Expand Down Expand Up @@ -101,6 +102,37 @@ public void GetHashCode_should_return_zero()
result.Should().Be(0);
}

[Fact]
public void Serialize_null_should_write_null()
{
var serializer = new ConcreteIEnumerableSerializerBase<IEnumerable<int>, int>(Int32Serializer.Instance);
var document = new BsonDocument();
using var writer = new BsonDocumentWriter(document);
var context = BsonSerializationContext.CreateRoot(writer);
writer.WriteStartDocument();
writer.WriteName("x");

serializer.Serialize(context, new BsonSerializationArgs(), null);

writer.WriteEndDocument();
document["x"].Should().Be(BsonNull.Value);
}

[Fact]
public void Deserialize_null_should_return_default()
{
var serializer = new ConcreteIEnumerableSerializerBase<IEnumerable<int>, int>(Int32Serializer.Instance);
var document = new BsonDocument("x", BsonNull.Value);
using var reader = new BsonDocumentReader(document);
reader.ReadStartDocument();
reader.ReadName("x");
var context = BsonDeserializationContext.CreateRoot(reader);

var result = serializer.Deserialize(context, new BsonDeserializationArgs { NominalType = typeof(IEnumerable<int>) });

result.Should().BeNull();
}

@BorisDog BorisDog May 26, 2026 •
edited
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Would be good to have some limited end-to-end testing. By "e2e" here I mean serializing and deserializing a real POCO, using a real expression (without DB).
But not sure where we place such tests now, any ideas @sanych-sun?

@sanych-sun sanych-sun May 26, 2026

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It probably should be a Theory with bytes on one side and expected value on the another. We might need such for all serializers.


internal class ConcreteIEnumerableSerializerBase<TEnumerable, TItem> : IEnumerableSerializerBase<TEnumerable, TItem>
where TEnumerable : IEnumerable<TItem>
{
Expand Down