"Array" settings get misleading formatting for default values and error reporting

From the user's perspective, the new ":array" settings type is just a comma separated list, like we use in existing settings like dns_alt_names or tags. But the default values and error reporting for the disable_warnings setting aren't formatted with this in mind, and are presented in a confusing fashion:

Error: Could not initialize global default settings: Cannot disable unrecognized warning types ["stuff"]. Valid values are ["deprecations"].

See also the config reference, which shows the default value as "[]". (http://docs.puppetlabs.com/references/latest/configuration.html#disablewarnings)

If you try to follow these hints and give a value like [deprecations], you get:

Error: Could not initialize global default settings: Cannot disable unrecognized warning types ["[deprecations"]"]. Valid values are ["deprecations"].

Boo. The UI is a comma-separated list without brackets, so any error or information reporting should present that same UI.