It returns [document, 0] to [document,0]. This causes firstRectForCharacterRange:[0,0] to return a rect outside the body. See: editing/input/range-for-empty-document.html
Do we still need to track this - we still have this test: https://github.com/WebKit/WebKit/blob/689b0ba375c8ad009024dac56d3d7713c6f5b7c6/LayoutTests/editing/mac/input/range-for-empty-document.html