fix: Align TestOrchestrationClient null serialization with TaskHubGrpcClient#199

YunchuWang merged 1 commit intomainmicrosoft/durabletask-js:mainfrom

copilot-finds/bug/fix-test-client-null-serializationmicrosoft/durabletask-js:copilot-finds/bug/fix-test-client-null-serializationCopy head branch name to clipboard