This is self-explanatory:
[subbu@earth lib] cat /tmp/html
<a rel="mw:WikiLink" href="./Foo" title="Foo" data-parsoid='{}'>Foo</a>
[subbu@earth lib] node parse --fetchConfig false --html2wt < /tmp/html
[[./Foo]]That should have serialized as [[Foo]] which it does without the empty data-parsoid