Description

System.Text.Json is unable to deserialize FluentValidation.Results.ValidationResult, while Newtonsoft.Json is able to do it.

Reproduction Steps

Check this code in .NET 6:

var validationResult = new ValidationResult
{
    Errors = { new ValidationFailure("MyProperty", "Invalid MyProperty") }
};
// System.Text.Json
var serialized = JsonSerializer.Serialize(validationResult);
var deserialized = JsonSerializer.Deserialize<ValidationResult>(serialized);

// Newtonsoft.Json
var serialized2 = JsonConvert.SerializeObject(validationResult, Formatting.Indented);
var deserialized2 = JsonConvert.DeserializeObject<ValidationResult>(serialized2);

The deserialized variable contains a ValidationResult object with IsValid = true, and 0 Errors.
The deserialized2 variable contains a ValidationResult object with IsValid = false, and 1 Error.

The serialization operation produces an identical json string for both libraries, but the System.Text.Json fails to deserialize it back to a ValidationResult object.

Expected behavior

The Error properties should be deserialized.

Actual behavior

The Error properties are not deserialized.

Regression?

I am not sure. I only tested it in .NET 6 (LTS).

Known Workarounds

Using Newtonsoft Json instead...

Configuration

OS: Windows 10
.NET version: 6.0.202
Architecture: x64

Other information

I found this old issue on the FluentValidation repo: FluentValidation/FluentValidation#719.
They described there what was the issue when no library was able to deserialize from json to ValidationResult, but that issue was fixed and Newtonsoft Json works properly.