[TYPO3] Render MENU differently IF abstract-field content

[T.Joga]

Hi! I have o problem rendering my subnavigation menu - it works ok, but 
I would like to get data from pages abstract field and put that text 
over my menu-item. This works, ...but when I add style to that extra 
text this style is rendered on every cell - also the empty ones. Is 
there a way to add style only the cells that have some content?:
This is the current menu:

temp.sub_navi = HMENU
temp.sub_navi.entryLevel = 2
temp.sub_navi.1 = TMENU
temp.sub_navi.1.noBlur = 1
temp.sub_navi.1 {
   NO{
   	allWrap = <li>|</li>
   }
   ACT = 1
   ACT.allWrap = <li class="subnavi-act">|</li>
}
temp.sub_navi.1.NO.before.field = abstract
temp.sub_navi.1.NO.before.wrap = <div id="abstract">|</div>
temp.sub_navi.1.ACT.before.field = abstract
temp.sub_navi.1.ACT.before.wrap = <div id="abstract-act">|</div>

temp.sub_navi.2 < temp.sub_navi.1
temp.sub_navi.3 < temp.sub_navi.2


this is something I tried with no success:

temp.sub_navi.1.ACT.before.if {
value.data = abstract
   isTrue.field = abstract
   field = abstract
   wrap = <div id="abstract-act">|</div>
   negate = 1
}