I think it should be something like this in 'removePlaceholder' method:
root.setHtml( editor.enterMode === CKEDITOR.ENTER_P ? '<p><br/></p>' : (editor.enterMode === CKEDITOR.ENTER_DIV ? '<div><br/></div>' : '<br/>') );
And if so, 'dataIsEmpty' should have condition for <div>
I think it should be something like this in 'removePlaceholder' method:
And if so, 'dataIsEmpty' should have condition for
<div>