Spring Mockito Syntax error on token "boolean", Dimensions expected after this token

I'm having a problem with my Unit Test that implies my Service class in my application involing the Dao.

@Mock(answer = Answers.RETURNS_DEEP_STUBS) 
private AvisDao avisDao;

@InjectMocks
private ApiPortalsService service = new ApiPortalsServiceImpl();   

@Before
public void initMocksWS() throws Exception{
    MockitoAnnotations.initMocks(this);
}

Factory factoria = FactoryImpl.getInstance();

@Test
public void testGuardarAvisos() throws Exception{
    Mockito.when(avisDao.existsPortalContingut(AvisPortal.class.cast(Matchers.anyObject()))).thenAnswer(new Answer<boolean>(){
        @Override
        public boolean answer(InvocationOnMock invocation) throws Throwable{                             

            return true; 
        }
    });
}

Here is the Test class, the error is occuring when I try to set the thenAnswer with a boolean. The method existsPortalContingut that contains an object returns a boolean. This is the first time I'm trying to create a Test class if I forget something, please tell me and I'll edit it.

What I am declaring wrong?

boolean existsPortalContingut(final AvisPortal portalContenido);   

This is the method I'm trying to call in the Dao