another way to display the $null check is using a ! before your check so the

if (%lf_flood. [ $+ [ $nick ] ] == $null)

could be changed to

if (!%lf_flood. [ $+ [ $nick ] ] )

and it will work the same. Personally I prefer using the ! as it saves space and works easier on my eyes. But this depends on the user/writer. each has a preference they use. So either (identifier == $null) or (!identifier)