juju default config string value of 'null' produces an error

[Andrew Glen-Young]

I was creating a new config option for a charm and wanted to have a default string option of 'null' (without the quotes) as documented on 'service-config' page[1] on the juju site.

This results in juju telling me that I have an invalid option.

Either the documentation needs to be updated or there is a regression?

Example config.yaml:

  default-roles:
    default: null
    type: string
    description: |
      Comma separated list of roles to create (other than admin-role).

Snippet of the config on the juju site:

  options:
      blog-roll:
          default: null
          description: List of URLs which will be included as the blog roll

Error message:

2013-01-18 23:18:27,875 WARNING Charm 'keystone~' has an error: ServiceConfigError() Error processing '/home/a
gy/tmp/charms/precise/keystone~/config.yaml': Invalid options specification: options.default-roles.default: expected string, got None

System information:

$ dpkg-query --show juju
juju 0.6.0.1+bzr608-0juju2~precise1

[1]: https://juju.ubuntu.com/docs/drafts/service-config.html

[Javier López (javier-lopez)]

From http://irclogs.ubuntu.com/2011/12/06/%23juju.html#t20:08

It seems the 'null' in the documentation should be replaced with ""

[Kapil Thangavelu (hazmat)]

not sure that's an error. 'null' is the yaml serialization of None/nil .. and the validation is for a string type. we could transparently substitute an empty string as the default value in this case without changing the semantics though.

[Javier López (javier-lopez)]

Yeah, I think it would be cool to use the correct semantic 'null' and replace "" for it, however right now (and since 2011), if you want to have a blank option "" is the only way to go =/