IgnoreNullValues isn't for deserialization

[tdykstra]

Fixes dotnet/docs#23450

[gewarren]

Should you also add a remark in the remarks section that it does not apply to deserialization?

[opbld31]

Docs Build status updates of commit f8fe2b0:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Text.Json/JsonSerializerOptions.xml	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the docs.microsoft.com contributor guides
• Post your question in the Docs support channel

[tdykstra]

@gewarren Thanks for the review!

[opbld31]

Docs Build status updates of commit 54626e7:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Text.Json/JsonSerializerOptions.xml	✅Succeeded	View

For more details, please refer to the build report.

Note: Broken links written as relative paths are included in the above build report. For broken links written as absolute paths or external URLs, see the broken link report.

For any questions, please:

• Try searching the docs.microsoft.com contributor guides
• Post your question in the Docs support channel

[layomia]

Actually, IgnoreNullValues is honored when deserializing. We did this for compat with Newtonsoft.Json (NullValueHandling) in v1 (.NET Core 3.x), but ended up obsoleting it after introducing DefaultIgnoreCondition in .NET 5.

DefaultIgnoreCondition (currently) only applies to serialization. When designing the new option, we couldn't think of a good reason to ignore null values in JSON payloads when reading. Most Newtonsoft.Json users don't even know that NullValueHandling is honored when deserializing. We decided not to carry over the "mistake" we made with IgnoreNullValues.