The manual page says:

The field events is an input parameter, a bit mask specifying the events the application is interested  in  for  the  file descriptor fd.  If this field is specified as zero, then all events are ignored for fd and revents returns zero.


However, this is not what happens.  POLLHUP and POLLERR are always reported (as one would expect, actually).

Test case 1:

#include <poll.h>
int main(void)
{
	struct pollfd pfd = { .fd = 0 };
	sleep(1);
	poll(&pfd, 1, 0);
}

$ echo x > fifo & strace -e poll ./a.out < fifo
poll([{fd=0, events=0}], 1, 0) = 1 ([{fd=0, revents=POLLHUP}])


Test case 2:

#include <poll.h>
int main(void)
{
	struct pollfd pfd = { .fd = 1 };
	sleep(1);
	poll(&pfd, 1, 0);
}


$ :< fifo & strace -e poll ./a.out > fifo
poll([{fd=1, events=0}], 1, 0) = 1 ([{fd=1, revents=POLLERR}])