Exclusion not working

[cici]

I have a test which is implemented as:

given:
final Class<Principal> classUnderTest = Principal.class
final Predicate<String> predicate = exclude("countriesOfCitizenship", "contact")
expect:
assertPojoMethodsFor(classUnderTest, predicate).areWellImplemented()

And I get this error:

Class blah.domain.Principal has bad 'toString' method implementation.
The toString method should contain:
countriesOfCitizenship=[]
But does not.

Is my syntax incorrect or is there a bug?

[cici]

Turns out this was a difference with Groovy strings and I had to use single-quotes.