global foo
probe begin {
        printf("foo[1] = %d %d\n", @count(foo[1]), @sum(foo[1]))
        exit()
}

generates code like this:
l->__tmp1 = _stp_pmap_get_ix (global_foo, l->__tmp3);
l->__tmp2 = l->__tmp1->count;

Problem is that foo[1] doesn't exist so _stp_pmap_get_ix returns NULL.