When container is document, cleanup steps fails with "TypeError: Cannot read properties of null (reading 'removeChild')"

Just opening this for tracking with the associated PR: #1330 .

When:

render(<Component />, { container: document });

(Untested: This bug may require that Component render a <body> element.)

Then:

TypeError: Cannot read properties of null (reading 'removeChild')

Because:

// pure.js
    if (container.parentNode === document.body) {
      document.body.removeChild(container);
    }

If we first check that document.body is not null, then this error will not occur.

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