Missing Method Exception in Integration Tests for domain with constraint unique: true on save in BootStrap

When saving a domain with a constraint unique: true in from the Bootstrap during integration tests, a groovy.lang.MissingMethodException is thrown.

Run "test-app" on the attached project. Unit test will fail (didn't change it), then a missingMethodException is thrown from the Bootstrap.

Does not happen when unit tests are not run against the class with the constraint. (See the second bug report.)