empty element in 'structure'.

Some of my functions use what is in practice a structure tho in theory I 
guess it's just a collection of scalars and arrays, but it's all copied 
in one go like this:

     set -A IN "${(@Pkv)1}" # Copy the array to IN, the working copy.

... anyway it's very fragile, the 'structure' must never change, so even 
when a given 'element' isn't used, it must exist.  Here's a slice of one 
such structure:

  body[window]="Body"
  body[list]="body_list"
  body[page_tops]="Btops"

  Bclicks=()
  body[mouse_clicks]="Bclicks"
# body[mouse_clicks]="()"

  body[hight]=$((Hight))
  body[width]=$BW

... now here's the issue: 'body[mouse_clicks]' isn't used but again, it 
must exist otherwise the 'set' command above crashes. If I use the 
rather phony:

  Bclicks=()
  body[mouse_clicks]="Bclicks"

... it works fine.  But if I cut to the chase and do:

   body[mouse_clicks]="()"

... it doesn't work, the 'structure' fails cuz the 'element' vanishes -- 
I think.  Purely as a question of semantics is there a way to do it the 
'direct' way and avoid the placeholder 'Bclicks'? I know there's ways of 
hanging on to empty elements in an normal array and I thought the 
quotes  "()" would do it, but nada.  Or is this pushing zsh where she 
doesn't want to go? That is, preserving an entire empty array withing a 
pseudo structure? But again, doing it the 'long way' works fine.