`SFTPFileSystem.ls()` in root directory hides names

Consider the following methods

@staticmethod
def _decode_stat(stat, parent_path=None):
    if S_ISDIR(stat.st_mode):
        t = "directory"
    elif S_ISLNK(stat.st_mode):
        t = "link"
    else:
        t = "file"
    out = {
        "name": "",
        "size": stat.st_size,
        "type": t,
        "uid": stat.st_uid,
        "gid": stat.st_gid,
        "time": datetime.datetime.utcfromtimestamp(stat.st_atime),
        "mtime": datetime.datetime.utcfromtimestamp(stat.st_mtime),
    }
    if parent_path:
        out["name"] = "/".join([parent_path.rstrip("/"), stat.filename])
    return out

def ls(self, path, detail=False):
    logger.debug("Listing folder %s" % path)
    stats = [self._decode_stat(stat, path) for stat in self.ftp.listdir_iter(path)]
    if detail:
        return stats
    else:
        paths = [stat["name"] for stat in stats]
        return sorted(paths)

And now suppose we want to run fs.ls(""), where "" is the root marker for SFTPFileSystem. The crucial part is here, in _decode_stat. Note that we are calling self._decode_stat(state, parent_path="")

out = {
    "name": "",
    "size": stat.st_size,
    "type": t,
    "uid": stat.st_uid,
    "gid": stat.st_gid,
    "time": datetime.datetime.utcfromtimestamp(stat.st_atime),
    "mtime": datetime.datetime.utcfromtimestamp(stat.st_mtime),
}
if parent_path:  # <-- This evaluates to false when parent_path=""
    out["name"] = "/".join([parent_path.rstrip("/"), stat.filename])

The result is that all the items in the root directory come back as ["", "", "". ...]. The condition should likely be if parent_path is not None:

Start at SFTPFileSystem._decode_stat and ls, using the issue's reproduction fs.ls("") to inspect the root-directory listing. Done means the returned names contain each root item rather than repeated empty strings, while preserving the existing detailed and sorted listing behavior.