Blocks#render doesn't work (API)

Hello. I have a basic editorJS setup, with only the header tool and a testtool. I’m trying to use the blocks#render function in the API. This is my tool.

class MyTool {
  constructor({data, api}){
    this.api = api;
    // ...
    setTimeout(() => {
      this.test();
    }, 1000);
  }

  test() {
    this.api.blocks.render(
      [
        {
          type: "header",
          data: {
             text: "New header",
             level: 2
          }
        }
      ]
    );
  }
}

It’s almost a direct copy from the docs.

When I load the page, everything is fine. After one second the function “test” is called and the editor is blank.

I get this error in my console.

Uncaught (in promise) TypeError: Cannot read property 'map' of undefined
    at e.<anonymous> (editorjs@latest:6)
    at c (editorjs@latest:6)
    at Generator._invoke (editorjs@latest:6)
    at Generator.forEach.t.<computed> [as next] (editorjs@latest:6)
    at c (editorjs@latest:6)
    at e (editorjs@latest:6)
    at editorjs@latest:6
    at new Promise (<anonymous>)
    at r (editorjs@latest:6)
    at S._invoke (editorjs@latest:6)

Am I doing something wrong or is this a bug?

[findela]

The documentation site of this plugin is limited, unclear, less example oriented, more worried and very poor in knowledge base. It’s only super-heroic to ninja people or for those stupid folks who built this.

[Paultje52]

@psdon is editor.js ready before you try it?