mountpoint-util: make path_get_mnt_id_at() work with a NULL path

src/basic/mountpoint-util.c

@@ -63,7 +63,7 @@ int name_to_handle_at_loop(
 
                 h->handle_bytes = n;
 
-                if (name_to_handle_at(fd, path, h, &mnt_id, flags) >= 0) {
+                if (name_to_handle_at(fd, strempty(path), h, &mnt_id, flags) >= 0) {
 
                         if (ret_handle)
                                 *ret_handle = TAKE_PTR(h);
@@ -362,11 +362,10 @@ int path_get_mnt_id_at(int dir_fd, const char *path, int *ret) {
         int r;
 
         assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
-        assert(path);
         assert(ret);
 
         if (statx(dir_fd,
-                  path,
+                  strempty(path),
                   (isempty(path) ? AT_EMPTY_PATH : AT_SYMLINK_NOFOLLOW) |
                   AT_NO_AUTOMOUNT |    /* don't trigger automounts, mnt_id is a local concept */
                   AT_STATX_DONT_SYNC,  /* don't go to the network, mnt_id is a local concept */