How to Mock ProceedingJoinPoint

I am trying to writing a Spock specification that test an AspectJ advice class. Therefore I need a mock instance of org.aspectj.lang.ProceedingJoinPoint class.

void "Verify client capability mechanism"() {

   given:
   def pointCut = Mock(ProceedingJoinPoint)

   and: 'the method calls would have the following arguments'
   pointCut.getArgs() >> ['xxx', 1L, 44] as Object[] // this is where the error happens

   when: 'the advice gets called'
   def retVal = new ClientCapabilitySecurityAdvice().verifyUserCanPerformActionOnCurrentClient(pointCut)

   then: 'the call may proceed'
   1 * pointCut.getArgs()
   1 * pointCut.proceed() >> 'Hello'
   retVal == 'Hello'
}

For some reason I am not able to define a return value on getArgs() on my mock instance. I get this error message.

java.lang.NullPointerException: Cannot invoke method rightShift() on null object

What is the proper way to mock the ProceedingJointPoint interface? Can someone help me on this?

PS: Merry christmas to you :)