Snapshot on mountpoint "/" is not working

[buck5060]

I was trying to snapshot on moutpoint / by using command /root/btrfs-snap/btrfs-snap / 10min 12
And I get following error message (with set -x)

+ mp=
+ prefix=daily
+ cnt=1
+ mount -t btrfs
+ cut -d ' ' -f 3
+ grep '^$'
+ '[' 1 -ne 0 ']'
+ btrfs subvolume show
+ grep '$'
btrfs subvolume show: too few arguments
usage: btrfs subvolume show [options] <subvol-path>|<mnt>

    Show more information about the subvolume

    -r|--rootid   rootid of the subvolume
    -u|--uuid     uuid of the subvolume

    If no option is specified, <subvol-path> will be shown, otherwise
    the rootid or uuid are resolved relative to the <mnt> path.

+ '[' 1 -ne 0 ']'
+ log.error ' is not a btrfs mountpoint (or old version of btrfs-tools, try > 0.19)'
+ logger -p local0.err -t btrfs-snap ' is not a btrfs mountpoint (or old version of btrfs-tools, try > 0.19)'
+ echo 'ERROR:  is not a btrfs mountpoint (or old version of btrfs-tools, try > 0.19)'
ERROR:  is not a btrfs mountpoint (or old version of btrfs-tools, try > 0.19)
+ exit 1

I found that PR #17 solve this issue
It will be great if the patch is merged.

Thanks :)