Criteria query unit test fails for composite id

### Steps to Reproduce
- Clone linked github repository and run unit tests
### Expected Behaviour

Given this domain class:

```

class PersistenceRolesToBeGranted implements Serializable {

String username

String authority

static constraints = {
username nullable: false, email: true
authority nullable: false
}

static mapping = {
id composite: ['username', 'authority'], generator: 'assigned'
version false
}
}

```

and service:

```
import grails.transaction.Transactional

@Transactional
class PersistenceRolesToBeGrantedGORMService {
List findAllAuthorityByEmail(String email) {
def c = PersistenceRolesToBeGranted.createCriteria()
c.list {
projections {
property('authority')
}
eq('username', email)
} as List
}
}

```

I expect this unit test to pass:

```
import grails.test.mixin.Mock
import grails.test.mixin.TestFor
import spock.lang.Ignore
import spock.lang.Specification

@TestFor(PersistenceRolesToBeGrantedGORMService)
@Mock([PersistenceRolesToBeGranted])
class PersistenceRolesToBeGrantedGORMServiceSpec extends Specification {

def "test findAllAuthorityByEmail"() {
given:
new PersistenceRolesToBeGranted(username: 'sergio.delamo@hola.com', authority: 'ROLE_ADMIN').save()

expect:
['ROLE_ADMIN'] == service.findAllAuthorityByEmail('sergio.delamo@hola.com')
}
}

```
### Actual Behaviour

The unit test fails. If I comment out the`composite` line on the domain class it passes
### Environment Information
- **Operating System**: OSX
- **Grails Version:** 3.1.11
- **JDK Version:** 1.8.0_45
### Example Application

[Github Repo](https://github.com/sdelamo/grails-issues-composite-id-fail-unit)

Clone the linked example application and run its unit tests first. Inspect PersistenceRolesToBeGranted, PersistenceRolesToBeGrantedGORMService, and PersistenceRolesToBeGrantedGORMServiceSpec to isolate the composite-id criteria query failure. Done means the test passes while the composite mapping remains enabled.

Written by the indexing model from the issue text.