Newbie question: why doesn't restoring state with spawned childs work?

[JarnoBoks]

Hi, I'm new to xstate. I'm trying to incorporate xstate into my home automation system and running some tests. The idea is to make a general machine for the house status, which spawns machines for the resident statuses. I'm running some test for the general architecture. Works ok: I can setup the parent machine, which spawns the residents with some configuration parameters. I can send events to the main machine and to the child machines. The final step in my tests is the persistence. And that is where it fails:

If I persist and restore without spawning childs everything is ok, the machine restores in its peristed state.
But restoring the state when I have spawned a child results in an error "java.lang.NullPointerException: Cannot invoke "java.lang.Long.longValue()" because "delay" is null

(but I cannot find out where this error starts from).

Any clues how to get my machine persisting?

childmachine:

const simplemachine = createMachine(
  {
    id: "Untitled",
    initial: "First State",
    states: {
      "First State": {
        on: {
          next: [
            {
              target: "Second State",
              actions: [],
              meta: {},
            },
          ],
        },
      },
      "Second State": {},
    },
  },
  {
    actions: {},
    actors: {},
    guards: {},
    delays: {},
  },
);

parentmachine:

const parentmachine = createMachine(
  {
    id: "parent",
    entry: [
      {
        type: "setContext",
      },
      {
        type: "spawnResidents",
      },
    ],
    initial: "idle",
    states: {
      idle: {
        entry: {
          type: "Log",
        },
        on: {
          ACTIVATE: [
            {
              target: "active",
              actions: [],
            },
          ],
        },
      },
      active: {
        on: {
          TEST: [
            {
              target: "test",
              actions: [],
            },
          ],
        },
      },
      test: {
        entry: {
          type: "LogTest",
        },
        on: {
          STEP2: [
            {
              target: "STEPPED",
              actions: [],
            },
          ],
        },
      },
      STEPPED: {
        entry: {
          type: "LogStepped",
        },
      },
    },
    on: {
      "*": [
        {
          guard: "isForResident",
          actions: [
            {
              type: "forwardToChilds",
            },
          ],
        },
      ],
    },
  },
  {
    actions: {
      LogTest: function ({ context, event }, params) {
        console.log("Entering Test");
      },
      LogStepped: function ({ context, event }, params) {
        console.log("Stepped");
      },
      Log: function ({ context, event }, params) {
        // Add your action code here
        console.log("Log");
        console.log(context.invokedresidents);
      },
      spawnResidents: assign({
        childMachineRefs: ({ context, spawn }) => {
          let val = [];
          for (let i = 0; i < context.invokedresidents.length; i++) {
            val[i] = spawn(simplemachine, context.invokedresidents[i]);
          }
          return val;
        },
      }),
      setContext: assign(
        // Update the context items with event input object and set the isInitialised value to true.
        ({ _, event }) => event.input,
      ),
      forwardToChilds: sendTo(
        ({ context, event }) => {
          return event.resident;
        },
        ({ context, event }) => {
          return event;
        },
      ),
    },
    actors: {},
    guards: {
      isForResident: function ({ context, event }, params) {
        return event.resident && event.resident.length > 0;
      },
    },
    delays: {},
  },
);

Invocation:

let stateString = items.getItem(openhabMachineConfig.oh_item_machinestate).state;
if (openhabMachineConfig.ignoreState) stateString = "NULL";

const restoredState = (stateString && stateString != "NULL") ? JSON.parse(stateString) : undefined;  

// Create the machine with the restored state   
const actor = createActor(parentmachine, {		
    snapshot: restoredState,
    input: config_house,
});

Persisting (after sending some events):

// Persist the new state of the Machine
const persistedState = actor.getPersistedSnapshot();
items.getItem(openhabMachineConfig.oh_item_machinestate).postUpdate(JSON.stringify(persistedState));

Stored state (string):

{
  "status": "active",
  "value": "test",
  "historyValue": {},
  "context": {
    "invokedresidents": [
      {
        "id": "Jarno",
        "input": {
          "resident_name": "Jarno",
          "oh_item_home": "JarnoMobilephone_PresenceHome__google",
          "oh_item_vacation": "JarnoVacation__status",
          "oh_item_alarmclock": "JarnoMobilephone_AlarmClock__samsung",
          "Initialised": true
        }
      }
    ],
    "house_name": "Amersfoortseweg",
    "oh_item_illuminance": "BalconyRaindetector_Illuminance",
    "oh_tag_residentstates": "resident_state",
    "Initialised": true,
    "childMachineRefs": [
      {
        "xstate$$type": 1,
        "id": "Jarno"
      }
    ]
  },
  "children": {
    "Jarno": {
      "snapshot": {
        "status": "active",
        "value": "First State",
        "historyValue": {},
        "context": {},
        "children": {}
      },
      "src": {
        "id": "simplemachine",
        "key": "simplemachine",
        "type": "compound",
        "initial": {
          "target": [
            "#simplemachine.First State"
          ],
          "source": "#simplemachine",
          "actions": [],
          "eventType": null
        },
        "history": false,
        "states": {
          "First State": {
            "id": "simplemachine.First State",
            "key": "First State",
            "type": "atomic",
            "initial": {
              "target": [],
              "source": "#simplemachine.First State",
              "actions": [],
              "eventType": null
            },
            "history": false,
            "states": {},
            "on": {
              "next": [
                {
                  "target": [
                    "#simplemachine.Second State"
                  ],
                  "actions": [],
                  "meta": {},
                  "source": "#simplemachine.First State",
                  "reenter": false,
                  "eventType": "next"
                }
              ]
            },
            "transitions": [
              {
                "target": [
                  "#simplemachine.Second State"
                ],
                "actions": [],
                "meta": {},
                "source": "#simplemachine.First State",
                "reenter": false,
                "eventType": "next"
              }
            ],
            "entry": [],
            "exit": [],
            "order": 1,
            "invoke": [],
            "tags": []
          },
          "Second State": {
            "id": "simplemachine.Second State",
            "key": "Second State",
            "type": "atomic",
            "initial": {
              "target": [],
              "source": "#simplemachine.Second State",
              "actions": [],
              "eventType": null
            },
            "history": false,
            "states": {},
            "on": {},
            "transitions": [],
            "entry": [],
            "exit": [],
            "order": 2,
            "invoke": [],
            "tags": []
          }
        },
        "on": {},
        "transitions": [],
        "entry": [],
        "exit": [],
        "order": -1,
        "invoke": [],
        "tags": []
      }
    }
  }
}

[JarnoBoks]

Found my issue: childs should be spawned by reference and not inline.

[davidkpiano]

I can update the documentation if this is unclear.

[JarnoBoks]

Is it written somewhere? I didn't find it, but maybe I did not read the correct document?