Iframe receiving null attributes when working with CustomRender

[JHBitencourt]

Although the default iframe render works fine, both attributes and element parameters from CustomRender are aways null when using it with iframe:

Html(
  data:
      '<iframe src="https://google.com"></iframe>'
      '<iframe title="W3Schools Free Online Web Tutorials" src="https://www.w3schools.com/tags/demo_iframe_sandbox.htm"></iframe>'
      '<iframe width="560" height="315" src="https://www.youtube.com/embed/mfokPqeSNcw" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>',
  customRender: {
    'iframe' : (
        RenderContext context,
        Widget parsedChild,
        Map<String, String> attributes,
        dom.Element element,
    ) {
      print(element);
      print(attributes);
      return null;
    },
  }
)

flutter_html: ^1.1.1 and flutter_html: ^1.0.2

% fvm flutter doctor
FVM: Running version 1.22.2
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel unknown, 1.22.2, on Mac OS X 10.15.5 19F101, locale en-BR)
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
[✓] Xcode - develop for iOS and macOS (Xcode 11.3.1)
[✓] Chrome - develop for the web
[!] Android Studio (version 4.1)
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
[!] IntelliJ IDEA Ultimate Edition (version 2019.2.4)
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
[✓] Connected device (4 available)

This issue is similar to what #464 and #473 described, but I've opened a new one to be clear that the problem is when using iframe with CustomRender.