"Send" button is disabled when trying to send an event with custom data

[a-uz]

I already noticed two other issues (#222, #223) regarding the send button, but this issue seems different.

As mentioned in the title, "Send" button is disabled when trying to send an event with custom data.

To reproduce this you may use this machine:

import { createModel } from "xstate/lib/model";

const counterModel = createModel(
  {
    count: 1,
  },
  {
    events: {
      INCREMENT: (by: number) => ({ by }),
    },
  }
);

const counterMachine = counterModel.createMachine({
  id: "counter",
  context: counterModel.initialContext,
  on: {
    INCREMENT: {
      actions: counterModel.assign({
        count: (context, event) => context.count + event.by,
      }),
    },
  },
});

With this event:

{
  "type": "INCREMENT",
  "by": 1
}