Swift blcok-stroage with loopback create invalid /etc/fstab entry

When deploy swift-storage using loopback device, the /etc/fstab generated is invalid:

#juju deploy --to 0 --config swift-storage.yml swift-storage

Located charm "cs:swift-storage-240".
Deploying charm "cs:swift-storage-240".

#cat swift-storage.yml
swift-storage:
  block-device: "/swift-storage.img|15G"
  overwrite: "false"

#juju status

Model Controller Cloud/Region Version SLA
default juju-controller mymaas 2.3.4 unsupported

App Version Status Scale Charm Store Rev OS Notes
swift-storage 2.7.1 blocked 1 swift-storage jujucharms 240 ubuntu

Unit Workload Agent Machine Public address Ports Message
swift-storage/11* blocked idle 0 10.2.1.12 Missing relations: proxy

Machine State DNS Inst id Series AZ Message
0 started 10.2.1.12 8hfyhc xenial default Deployed

#juju ssh 0 cat /etc/fstab
UUID=2bae4b71-a432-49f3-a6ac-f52e01ad9dbc / ext4 defaults 0 0
UUID=fa83ddcc-0ad5-4994-ba97-ad770db74788 /boot ext4 defaults 0 0
/swap.img none swap sw 0 0
/swift-storage.img /srv/node/loop0 xfs loop, defaults 0 0
Connection to 10.2.1.12 closed.

#Looking carefully:
The /swift-storage.image line: "loop, defaults 0 0"
has a space in it.

It should be:
/swift-storage.img /srv/node/loop0 xfs loop,defaults 0 0 #without space between loop, and "default 0 0"

This problem will render the machine to enter into single user maintenance mode once reboot it.