Grails, Shiro, addToPermissions() error

I've been playing with Grails with an eye to using it on a new project.

Apache Shiro looks like a suitable security framework for me so I thought I'd use it right from the off. There is even a plugin for Grails to simplify installation.

I discovered that you still have to create your own shiro.jar from the shiro source - but that was relatively straight forward....

[... once I had downloaded a new version of Maven (Fedora 11 packaged version wasn't recent enough)....]

So, once I had installed shiro.jar, and the plugin, I decided to run:
'grails create-db-realm' and
'grails create-authcontroller'
and added bootstrap code according to the plugin advice

ASIDE: for the purposes of just playing around. A better choice for 'playing around' is to do:
'grails quick-start'

If you followed the same route as me, you may have experienced:

Caused by: groovy.lang.MissingMethodException: No signature of method: static groovy.lang.MissingMethodException.addToPermissions() is applicable for argument types: (java.lang.String) values: [*:*]

The fix I arrived at is to add the line:
static hasMany = [ roles: ShiroRole, permissions: String ]
to ShiroUser.groovy so it becomes:

class ShiroUser {
String username
String passwordHash

static hasMany = [ roles: ShiroRole, permissions: String ]

static constraints = {
username(nullable: false, blank: false)
}
}

This got me past this error, however since I feel that I still don't properly 'get it', I expect more issues (and possibably blog posts) in the future!