[release/8.0] Fix reading null struct property value in gRPC JSON transcoding

[github-actions]

Backport of #52442 to release/8.0

/cc @JamesNK

Fix reading null struct property value in gRPC JSON transcoding

Struct is a Protobuf type that represents JSON-like data, e.g.

• List
• Map
• String
• Bool
• Integer
• Null

Reading null values to a struct resulted in an error. We set a null reference when Struct requires Value of type null

The fix is to make the Value JSON converter handle null values, and then return a Value of type null to the struct.

Fixes #51521

Customer Impact

Apps are unable to send null values to a gRPC JSON transcoding server in struct values. They are either forced to change the client or are stuck if they can't.

There isn't a workaround.

Regression?

• Yes
• No

[If yes, specify the version the behavior has regressed from]

Risk

• High
• Medium
• Low

This is a minor change to the Microsoft.AspNetCore.Grpc.JsonTranscoding package. Nothing else in .NET depends on it.
Null values previously errored. This change only impacts the JsonConverter for the Value type.

Verification

• Manual (required)
• Automated

After:

Note: structValue has null/bool/string values.

Packaging changes reviewed?

• Yes
• No
• N/A

---

When servicing release/2.1

• Make necessary changes in eng/PatchConfig.props

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[ghost]

Hi @github-actions[bot]. This PR was just approved to be included in the upcoming servicing release. Somebody from the @dotnet/aspnet-build team will get it merged when the branches are open. Until then, please make sure all the CI checks pass and the PR is reviewed.

[JamesNK]

Email approval

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