Fold primary text of list item if blank

[mojavelinux]

If the primary text of the list item is blank, fold the first block into the first line so that it appear in line with the bullet/marker.

Example:

* {blank}
+
--
list item content
--

Additionally, if the primary text is blank, and the list item does not have any blocks (not complex), then insert placeholder text so that the margin does not collapse into the bullet/marker.

Example:

* {blank}