Runtime: System.Text.Json DictionaryKeyPolicy is ignored if entry value is null

[uncleyo]

When setting DictionaryKeyPolicy = JsonNamingPolicy.CamelCase;, only non-null value entries have their keys properly converted.

I believe it is because the key is only converted inside the else branch here.

I assume this is a bug, at least I cannot imagine this would be an expected and desired behavior.

[steveharter]

cc @layomia. Looks like when DictionaryKeyPolicy support was added, it only was added to the non-null value case.

[nickalbrecht]

I just ran into this as well. Makes for really inconsistent behaviour when trying to use the a Json result from asp.net core app because the Json object might be the expected case in instance and a different casing in another.

[ericstj]

Fixed in 3.1. Thanks for the report!

[uncleyo]

That was quick! Was considering to make this my own first contribution to the repo, but you've nailed it, people!

[ThorstenHans]

unfortunately, this issue still exists in 3.1.101 @ericstj

I have a simple POCO holding a dynamic property. If the most inner property has a value of null, JsonNamingPolicy.CamelCase is ignored:

var foo = new Poco
            {
                Name = "Hello NETCORE",
                Inner = new ExpandoObject()
            };

            foo.Inner.FieldA = null;
            foo.Inner.FieldB = "Field B Valu";
            foo.Inner.FieldC = false;

            var options = new JsonSerializerOptions
            {
                WriteIndented = true,
                DictionaryKeyPolicy = JsonNamingPolicy.CamelCase,
                PropertyNamingPolicy = JsonNamingPolicy.CamelCase
            };
            Console.WriteLine(JsonSerializer.Serialize(foo, options));

Which returns

{
  "name": "Hello NETCORE",
  "inner": {
    "FieldA": null,
    "fieldB": "Field B Valu",
    "fieldC": false
  }
}

in contrast to the expected result

{
  "name": "Hello NETCORE",
  "inner": {
    "fieldA": null,
    "fieldB": "Field B Valu",
    "fieldC": false
  }
}

csproj:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>
</Project>

sdk is version 3.1.101

[ericstj]

https://github.com/dotnet/corefx/pull/42284 added the fix to this original issue. @ThorstenHans It seems like this issue may be different. Could be related to https://github.com/dotnet/runtime/issues/29690. I don’t think we have support for ExpandoObject yet. Cc @layomia to double check.

[ThorstenHans]

@ericstj right there is no official support for ExpandoObject yet. However, I expect either an UnsupportedException.

Or if processed without any error, it should generate homogeneous JSON according to the configuration.