This kernel commit restored original behavior:
commit 1fa1e7f615f4d3ae436fa319af6e4eebdd4026a8
Author: Andy Whitcroft <apw@canonical.com>
Date:   Wed Nov 2 09:44:39 2011 +0100
     readlinkat: ensure we return ENOENT for the empty pathname for
normal lookups

For kernel >= 3.2, ENOENT should be expected errno code.

Signed-off-by: Jan Stancek <jstancek@redhat.com>
---
  testcases/kernel/syscalls/readlink/readlink03.c |    3 ++-
  1 files changed, 2 insertions(+), 1 deletions(-)