Schema of generic type: incorrect nullability

[Apollo3zehn]

I have the following setup to compare the schema of a non-generic type (A) to a generic version (A<B>) :

.csproj:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="NJsonSchema" Version="11.0.2" />
  </ItemGroup>

</Project>

Program.cs:

using NJsonSchema;

var nonGenericSchema = JsonSchema.FromType<A>();
var genericSchema = JsonSchema.FromType<A<B>>();

Console.WriteLine("Non-generic schema:");
Console.WriteLine(nonGenericSchema.ToJson());

Console.WriteLine("\n\nGeneric schema:");
Console.WriteLine(genericSchema.ToJson());

public record A
(
    B B
);

public record A<T>
(
    T B
);

public record B(string Value);

Unfortunately, in the generic version, the property B becomes nullable although it is not so in the C# type definition. Here is a comparison of both schemas:

Output:

Non-generic schema:
{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "title": "A",
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "B": {
      "oneOf": [
        {
          "type": "null"
        },
        {
          "$ref": "#/definitions/B"
        }
      ]
    }
  },
  "definitions": {
    "B": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "Value": {
          "type": "string"
        }
      }
    }
  }
}


Generic schema:
{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "title": "AOfB",
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "B": {
      "oneOf": [
        {
          "type": "null"
        },
        {
          "$ref": "#/definitions/B"
        }
      ]
    }
  },
  "definitions": {
    "B": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "Value": {
          "type": "string"
        }
      }
    }
  }
}

I think the reason is that there is no customAttributeProviders provided in the following call:

Namotion.Reflection/src/Namotion.Reflection/Context/ContextualType.cs

Line 28 in a4bc634

return new ContextualType(type, contextualAttributeProvider ?? new GenericTypeContext(Array.Empty<Attribute>()), null, ref index, null, null);

When this parameter is null, the call to InitializeNullableFlagsAndOriginalNullability ends with _emptyNullableFlags.

There is a big difference between both call stacks (non-generic vs generic) and the generic one leads to a call to GetCachedType which in turn passes null for the customAttributeProviders parameter.

I tried to debug it for hours (with a more complex type in the beginning) but I think more knowledge of the library internals is required to find the root cause. And I am not really sure if the bug is burried somewhere in this library or in NJsonSchema.