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SYSLIB0020: IgnoreNullValues is obsolete

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The JsonSerializerOptions.IgnoreNullValues property is marked as obsolete, starting in .NET 6. Using it in code generates warning SYSLIB0020 at compile time.

Workarounds

To ignore null values when serializing, set DefaultIgnoreCondition to JsonIgnoreCondition.WhenWritingNull. For more information, see https://github.com/dotnet/runtime/issues/39152.

Suppress a warning

If you must use the obsolete APIs, you can suppress the warning in code or in your project file.

To suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the warning.

// Disable the warning.
#pragma warning disable SYSLIB0020

// Code that uses obsolete API.
// ...

// Re-enable the warning.
#pragma warning restore SYSLIB0020

To suppress all the SYSLIB0020 warnings in your project, add a <NoWarn> property to your project file.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
   ...
   <NoWarn>$(NoWarn);SYSLIB0020</NoWarn>
  </PropertyGroup>
</Project>

For more information, see Suppress warnings.