ArgumentNullException in System.Text.Json.Serialization.Metadata.JsonTypeInfo

[JakenVeina]

Description

I am receiving an ArgumentNullException from JsonSerializer.Serialize<T>(Utf8JsonWriter, T value, JsonSerializerOptions options) that appears to be the result of a faulty null-check-override within JsonTypeInfo.

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/JsonTypeInfo.cs

Line 526 in 804a933

Name = reflectionInfo.Name!,

   at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.OrdinalIgnoreCaseComparer.GetHashCode(String obj)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo.ParameterLookupKey.GetHashCode()
   at System.Collections.Generic.Dictionary`2.FindValue(TKey key)
   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo.InitializeConstructorParameters(ConstructorInfo constructorInfo)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo..ctor(Type type, JsonConverter converter, Type runtimeType, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializerOptions.<RootBuiltInConvertersAndTypeInfoCreator>g__CreateJsonTypeInfo|107_0(Type type, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializer.GetTypeInfo(Type runtimeType, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializer.Serialize[TValue](Utf8JsonWriter writer, TValue& value, Type runtimeType, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializer.Serialize[TValue](Utf8JsonWriter writer, TValue value, JsonSerializerOptions options)
   at Modix.Host.EntryPoint.EndpointWriteOnlyJsonConverter.Write(Utf8JsonWriter writer, Endpoint value, JsonSerializerOptions options) in D:\Projects\JakenVeina\MODiX\MODiX.Host\EntryPoint.cs:line 90

The null value in question is coming from System.Reflection.ParameterInfo.Name, retrieved from the constructor of System.Runtime.CompilerServices.NullableContextAttribute.

The NullableContextAttribute instance is coming from Microsoft.AspNetCore.Http.Endpoint which is being passed to Microsoft.Extensions.Logging.ILogger.Log calls as TState state.

NullableContextAttribute is an internal and compiler-generated type, so it's been proving difficult to implement a workaround where I just skip or customize serialization of the type. It also strikes me as a slight design defect that all this work is being done to analyze this type for deserialization, when I am only attempting to serialize it, and have no intention of ever deserializing it.

Configuration

.NET SDK 6.0.100-preview.7.21379.14
System.Text.Json 6.0.0-preview.7.21377.19

[eiriktsarpalis]

Hi @JakenVeina, would it be possible to provide a minimal app that reproduces the issue? Thanks.

[JakenVeina]

It looks like a "minimal" reproduction might not be possible. I have replicated the scenario in a simple console program, using the same runtime and package versions, and the exception does not occur. I.E...

JsonSerializer.Serialize(writer, value, options);

...where value is a NullableContextAttribute object, which, when reflected upon, produces a ParameterInfo object with a Name value of null. This line throws in the full solution, but not in the console program. The options object is not meaningfully different between the two. I noticed there's a decent amount of static caching of JsonTypeInfo objects going on, so perhaps that's somehow the culprit?

I will attempt to clone my full application and trim as much out of it as possible, without affecting the exception that throws.

[JakenVeina]

Here we go: https://github.com/JakenVeina/DotnetRuntimeIssue58690

I identified the issue with reproducing it locally: I was inadvertently calling .Serialize<Attribute>() instead of .Serialize(), resulting in the library reflecting upon System.Attribute instead of System.Runtime.CompilerServices.NullableContextAttribute.

[eiriktsarpalis]

I can reproduce. Minimal reproduction:

using System;
using System.Reflection;
using System.Text.Json;

Type type = Assembly.GetExecutingAssembly().GetType("System.Runtime.CompilerServices.NullableContextAttribute")!;
object value = Activator.CreateInstance(type, (byte)0)!;
JsonSerializer.Serialize(value);

// Force generation of a NullableContextAttribute in this assembly
static string? MethodWithNullableAnnotations() => throw new NotImplementedException();

Throws

Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'obj')
   at System.OrdinalIgnoreCaseComparer.GetHashCode(String obj)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo.ParameterLookupKey.GetHashCode()
   at System.Collections.Generic.Dictionary`2.FindValue(TKey key)
   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo.InitializeConstructorParameters(JsonParameterInfoValues[] jsonParameters)
   at System.Text.Json.Serialization.Metadata.JsonTypeInfo..ctor(Type type, JsonConverter converter, Type runtimeType, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializerOptions.<InitializeForReflectionSerializer>g__CreateJsonTypeInfo|112_0(Type type, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializerOptions.GetClassFromContextOrCreate(Type type)
   at System.Text.Json.JsonSerializerOptions.GetOrAddClass(Type type)
   at System.Text.Json.JsonSerializer.GetTypeInfo(JsonSerializerOptions options, Type runtimeType)
   at System.Text.Json.JsonSerializer.Serialize[TValue](TValue value, JsonSerializerOptions options)

I did not deduce the root cause -- for some reason attempting to replicate the implementation of NullableContextAttribute in source resulted in a different type of failure much later in the implementation. We should still investigate and at least attempt to fail more gracefully if this scenario cannot be supported.

This seems like a very niche use case. Moving to 7.0.0.