! { dg-do run }
character(len=1) :: s
character(len=0) :: s0
s = " "
s0 = ""
call bar ("")
call bar (s)
call bar (s0)
call bar (trim(s))
call bar (min(s0,s0))
contains
subroutine bar (s)
character(len=*), optional :: s
if (.not. present (S)) call abort
end subroutine bar
end