An empty line in a reply renders as:

::Foo
::
::Bar

It is likely that the user just didn't realise that in the reply tool context, double newlines are not required (as they are in a normal wikitext context) due to the indentation.

These empty list items are invisible, and likely not intended by the user, so it should be safe to remove them.

Example cases

//Below are instances of people who appear to be manually inserting extra blank lines in the middle of their reply.