reporting services - SSRS Conditional Border Report -

i have report table component. want apply following logic:

if value incid not null, border should "solid" (meaning should have border),
if value incid null, border should "none" (meaning table should have no border).

i used =iif(isnothing(fields!incid.value) = 1,"solid","none") doesn't work. problem? if apply , save settings , go expression, not saved.

ok, this seemed problem.