autodesk-forge - WorkItem の作成が失敗し、「オブジェクト参照がオブジェクトのインスタンスに設定されていません。」

Question

次の引数を使用して作業項目を作成すると、forge から内部エラーのように見えるものが表示されます。

{
  "error":{
    "code":"","message":"An error has occurred.","innererror":{
      "message":"Object reference not set to an instance of an object.","type":"System.NullReferenceException","stacktrace":"   at PublicApi.ResponseExceptionHelper.Throw(HttpStatusCode status, ModelStateDictionary state) in G:\\Repos\\IO\\src\\PublicAPI\\ResponseExceptionHelper.cs:line 31\r\n   at PublicApi.V2.Controllers.WorkItemsV2Controller.CreateEntity(WorkItem2 workItem) in G:\\Repos\\IO\\src\\PublicAPI\\V2\\Controllers\\WorkItemsV2Controller.cs:line 57\r\n   at PublicApi.V2.Controllers.BaseController`1.Post(TEntity entity) in G:\\Repos\\IO\\src\\PublicAPI\\V2\\Controllers\\BaseV2Controller.cs:line 62\r\n   at lambda_method(Closure , Object , Object[] )\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(Object instance, Object[] methodParameters)\r\n   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Tracing.ITraceWriterExtensions.<TraceBeginEndAsyncCore>d__18`1.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__0.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Tracing.ITraceWriterExtensions.<TraceBeginEndAsyncCore>d__18`1.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__2.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Tracing.Tracers.HttpControllerTracer.<ExecuteAsyncCore>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Tracing.ITraceWriterExtensions.<TraceBeginEndAsyncCore>d__18`1.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()"
    }
  }
}

これは、Forge に渡される次の JSON で発生します。(実際の値とは一部変更されています)

{
  "@odata.type": "#ACES.Models.WorkItem",
  "ActivityId": "CustomActivity",
  "Arguments": {
    "InputArguments": [
      {
        "HttpVerb": "GET",
        "Name": "HostDwg",
        "Resource": "https://s3.amazonaws.com/[path-redacted]",
        "ResourceKind": "ZipPackage",
        "StorageProvider": "Generic"
      },
      {
        "HttpVerb": "GET",
        "Name": "Request",
        "Resource": "https://s3.us-east-2.amazonaws.com/[path-redacted]",
        "ResourceKind": "ZipPackage",
        "StorageProvider": "Generic"
      }
    ],
    "OutputArguments": [
      {
        "HttpVerb": "POST",
        "Name": "GeneratedDrawing.dwg",
        "ResourceKind": "ZipPackage",
        "StorageProvider": "Generic"
      }
    ]
  },
  "Id": "",
  "UserID": "",
  "Version": 1
}

このコードのバリエーションをいくつでも試しました。他のフィールドを追加し、デフォルト値を含めました...しかし、これには何も渡されません。