AT_EMPTY_PATH works with empty strings (""), but not with NULL
(or at least it's not obvious).

The relevant kernel code is the following:

linux$ sed -n 189,198p fs/namei.c
	result->refcnt = 1;
	/* The empty path is special. */
	if (unlikely(!len)) {
		if (empty)
			*empty = 1;
		if (!(flags & LOOKUP_EMPTY)) {
			putname(result);
			return ERR_PTR(-ENOENT);
		}
	}

Reported-by: Walter Harms <redacted>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Adam Borowski <redacted>
Signed-off-by: Alejandro Colomar <redacted>
---
 man2/open.2 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/man2/open.2 b/man2/open.2
index 6360636af..bac1ee806 100644
--- a/man2/open.2
+++ b/man2/open.2

@@ -824,7 +824,7 @@ fd = open("/path/to/dir", O_TMPFILE | O_RDWR,
 
 /* File I/O on \(aqfd\(aq... */
 
-linkat(fd, NULL, AT_FDCWD, "/path/for/file", AT_EMPTY_PATH);
+linkat(fd, "", AT_FDCWD, "/path/for/file", AT_EMPTY_PATH);
 
 /* If the caller doesn\(aqt have the CAP_DAC_READ_SEARCH
    capability (needed to use AT_EMPTY_PATH with linkat(2)),

-- 
2.31.1