Spock & Spock Reports: how "catch" and customize the error message for AssertionError?

I am working with:

• Spock Core
• Spock Reports
• Spock Spring
• Spring MVC Testing

and I have the following code:

@FailsWith(java.lang.AssertionError.class)
def "findAll() Not Expected"(){

    given:

        url =  PersonaUrlHelper.FINDALL;

    when: 

        resultActions = mockMvc.perform(get(url)).andDo(print())

    then: 

        resultActions.andExpect(status().isOk())
                     .andExpect(content().contentType(MediaType.APPLICATION_XML))


}

Here the code fails (how is expected) because the method being tested really returns (MediaType.APPLICATION_JSON) instead of (MediaType.APPLICATION_XML).

So that the reason of @FailsWith(java.lang.AssertionError.class).

Even if I use @FailsWith(value=java.lang.AssertionError.class, reason="JSON returned ...") I am not able to see the reason through Spock Reports

Question One: how I can see the reason on Spock Reports?.

I know Spock offers the thrown() method, therefore I am able to do:

  then:
        def e = thrown(IllegalArgumentException)
        e.message == "Some expected error message"
        println e.message

Sadly thrown does not work for AssertionError.

If I use thrown(AssertionError) the test method does not pass, unique way is through @FailsWith but I am not able to get the error message from AssertionError

Question Two how is possible get the Error Message from AssertionError?

I know I am able to do something like

then: "Something to show on Spock Reports"

But just curious if the question two can be resolved..