Bot Framework Composer handoff request error

I can't seem to successfully send a handoff request in Bot Framework Composer. On clicking "Start bot" I get the error Error: Dialog.onComputeId(): not implemented. Full error log:

Error occurred building the bot

Error: Dialog.onComputeId(): not implemented. 
at SendHandoffActivity.onComputeId (C:\Users\User\Handoff\Handoff\node_modules\botbuilder-dialogs\lib\dialog.js:336:15) 
at SendHandoffActivity.get id [as id] (C:\Users\User\Handoff\Handoff\node_modules\botbuilder-dialogs\lib\dialog.js:133:29) 
at C:\Users\User\Handoff\Handoff\node_modules\botbuilder-dialogs-adaptive\lib\actions\actionScope.js:276:57 
at Array.map (<anonymous>) 
at ActionScope.onComputeId (C:\Users\User\Handoff\Handoff\node_modules\botbuilder-dialogs-adaptive\lib\actions\actionScope.js:276:34) 
at ActionScope.get id [as id] (C:\Users\User\Handoff\Handoff\node_modules\botbuilder-dialogs\lib\dialog.js:133:29) 
at DialogSet.add (C:\Users\User\Handoff\Handoff\node_modules\botbuilder-dialogs\lib\dialogSet.js:126:71) 
at C:\Users\User\Handoff\Handoff\node_modules\botbuilder-dialogs-adaptive\lib\adaptiveDialog.js:140:75 
at Array.forEach (<anonymous>) 
at AdaptiveDialog.ensureDependenciesInstalled (C:\Users\User\Handoff\Handoff\node_modules\botbuilder-dialogs-adaptive\lib\adaptiveDialog.js:140:43)

The bot is an empty bot with a "Send a handoff request" in "Unknown intent". Full bot code:

{
  "$kind": "Microsoft.AdaptiveDialog",
  "$designer": {
    "name": "Handoff",
    "description": "",
    "id": "A79tBe"
  },
  "autoEndDialog": true,
  "defaultResultProperty": "dialog.result",
  "triggers": [
    {
      "$kind": "Microsoft.OnConversationUpdateActivity",
      "$designer": {
        "id": "376720"
      },
      "actions": [
        {
          "$kind": "Microsoft.Foreach",
          "$designer": {
            "id": "518944",
            "name": "Loop: for each item"
          },
          "itemsProperty": "turn.Activity.membersAdded",
          "actions": [
            {
              "$kind": "Microsoft.IfCondition",
              "$designer": {
                "id": "641773",
                "name": "Branch: if/else"
              },
              "condition": "=string(dialog.foreach.value.id) != string(turn.Activity.Recipient.id)",
              "actions": [
                {
                  "$kind": "Microsoft.SendActivity",
                  "$designer": {
                    "id": "859266",
                    "name": "Send a response"
                  },
                  "activity": "${SendActivity_Greeting()}"
                }
              ]
            }
          ]
        }
      ]
    },
    {
      "$kind": "Microsoft.OnUnknownIntent",
      "$designer": {
        "id": "mb2n1u"
      },
      "actions": [
        {
          "$kind": "Microsoft.SendHandoffActivity",
          "$designer": {
            "id": "74xAHm"
          },
          "context": {
            "context": "c"
          },
          "transcript": {
            "transcript": "t"
          }
        }
      ]
    }
  ],
  "generator": "Handoff.lg",
  "id": "Handoff",
  "recognizer": "Handoff.lu.qna"
}

I haven't found anything on Google/Stack Overflow. Any help would be appreciated.