gRPC JSON transcoding — Fixed parsing string values into enum when provided string is not valid enum value

[zorix]

Fixed parsing string values into enum when provided string is not valid enum value

• You've read the Contributor Guide and Code of Conduct.
• You've included unit or integration tests for your change, where applicable.
• You've included inline docs for your change, where applicable.
• There's an open issue for the PR that you are making. If you'd like to propose a new feature or change, please open an issue to discuss the change or find an existing issue.

NullReferenceException is thrown when string value cannot be converted to gRPC enum value.

Description

Right now when we provided JSON string value (for example INVALID) into gRPC enum like this (I took it from tests)

enum NestedEnum {
  NESTED_ENUM_UNSPECIFIED = 0;
  FOO = 1;
  BAR = 2;
  BAZ = 3;
  NEG = -1;  // Intentionally negative.
}

We will get NullReferenceException in this line because valueDescriptor won't be found.

Not related issue found

[ghost]

Thanks for your PR, @zorix. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[zorix]

@dotnet-policy-service agree

[JamesNK]

Looks good to me. Some minor changes to the error message and variable names.

[JamesNK]

Thanks!