Whichever field you think is not compulsory or can have a null value, include a magnet tag like following :
[l.co;magnet=w:p]
Here magnet is a conditional which deletes the tag if the value is null or empty. It is having the value "w:p" because DOCX's XML file contains all the new values in a tag like :-
<w:p>...</w:p>
So it will delete the tag and whitespace will be removed.