Currently, it is not possible to have an empty list item, for example, in:
* A * * B
or in:
# A # # B
The middle list item will be removed. We (the parsing team) would like to change that, since it is counter-intuitive and makes things difficult for VisualEditor.
The challenge is that we suspect some templates are taking advantage of the removal of empty list items, as a shortcut to omit a list item when a parameter is empty. Such templates will have to be migrated to explicitly omit the affected list items. So we are planning on introducing logging and tools which will allow this problem to be quantified and fixed.
A change was recently merged which causes empty list items to be hidden with CSS, instead of removing them altogether. This change will be deployed next week as part of the usual weekly release train. This should not cause any visible changes. However it does enable client-side tools to be developed which will show an article with empty list items included, the way we imagine it will ultimately be rendered.
For more information, see: https://gerrit.wikimedia.org/r/#/c/246148/ https://phabricator.wikimedia.org/T49673
-- Tim Starling