MaaS 2.5.3: CentOS6 MaaS install having curtin error

I'm trying to deploy CentOS6 using MaaS. The CentOS6 image is not customised, and the setup has no problem deploying Ubuntu 18, CentOS7. When it was deploying CentOS6, it is having the following curtin error.

Stdout: start: cmd-install/stage-curthooks/builtin/cmd-curthooks: curtin command curthooks
        running /tmp/tmp_zvit2yw/target/curtin/curtin-hooks
        Running command ['/tmp/tmp_zvit2yw/target/curtin/curtin-hooks'] with allowed return codes [0] (capture=False)
        Traceback (most recent call last):
          File "/tmp/tmp_zvit2yw/target/curtin/curtin-hooks.py", line 393, in <module>
            main()
          File "/tmp/tmp_zvit2yw/target/curtin/curtin-hooks.py", line 376, in main
            grub_root = get_grub_root(target)
          File "/tmp/tmp_zvit2yw/target/curtin/curtin-hooks.py", line 208, in get_grub_root
            return regex.groups()[0]
        AttributeError: 'NoneType' object has no attribute 'groups'
        finish: cmd-install/stage-curthooks/builtin/cmd-curthooks: FAIL: curtin command curthooks
        Traceback (most recent call last):
          File "/curtin/curtin/commands/main.py", line 201, in main
            ret = args.func(args)
          File "/curtin/curtin/commands/curthooks.py", line 1287, in curthooks
            if util.run_hook_if_exists(target, 'curtin-hooks'):
          File "/curtin/curtin/util.py", line 883, in run_hook_if_exists
            subp([target_hook])
          File "/curtin/curtin/util.py", line 275, in subp
            return _subp(*args, **kwargs)
          File "/curtin/curtin/util.py", line 141, in _subp
            cmd=args)
        curtin.util.ProcessExecutionError: Unexpected error while running command.
        Command: ['/tmp/tmp_zvit2yw/target/curtin/curtin-hooks']
        Exit code: 1
        Reason: -
        Stdout: ''
        Stderr: ''
        Unexpected error while running command.
        Command: ['/tmp/tmp_zvit2yw/target/curtin/curtin-hooks']
        Exit code: 1
        Reason: -
        Stdout: ''
        Stderr: ''

Stderr: ''