Exception thrown when using domain classes with UUID(String) Primary Keys.

When i call
```
aclService.createAcl(
objectIdentityRetrievalStrategy.getObjectIdentity(report)
)
```
with the report domain having a UUID primary key, i get the exception,

`Argument [grails.plugin.springsecurity.acl.AclSid(sid:admin, principal:true, id:null, properties:[sid:admin, principal:true], dirty:false, dirtyPropertyNames:[], attached:false, errors:org.grails.datastore.mapping.validation.ValidationErrors: 0 errors)] is not an instance of [class grails.plugin.springsecurity.acl.AclSid] which this validator is configured for`

Anybody experienced this or has anybody used this plugin with String identifiers?

Start with the reported aclService.createAcl call and the validator exception when a domain class uses a UUID primary key. Reproduce the failure with a UUID(String) identifier and inspect the ACL validation path; done means ACL creation accepts the domain class without the reported type mismatch.

Written by the indexing model from the issue text.