Mockito error when mocking Request Dispatcher

I am using "GetRequestDispatcher" to be able to forward attributes between a servlet and a JSP page, like so(the following is taken from the servlet):

request.setAttribute("AttributeValue",message);
request.getRequestDispatcher("DestinationPage.jsp").forward(request, response);

I am now using Mockito to mock the HttpSession as well as the HttpRequest, HttpResponse and the Dispatcher, as follows:

@Test 
public void freeRiskAndAmountValidation() throws ServletException,IOException
{
    //given
    Mockito.doReturn("testAttr").when(session).getAttribute("A");
    Mockito.when(request.getRequestDispatcher("DestinationPage.jsp")).thenReturn(dispatcher);
    //when
    bets.doGet(request,response);
    //then
    Mockito.verify(dispatcher).forward(request,response);
}

However, my test returns a null pointer exception(console) AND mockito gives me the following error:

Wanted, but not invoked.
      dispatcher.forward(request,response);
Actually, there were zero interactions with this mock.

Could anyone tell me what is causing this error, and whether there is a better way of mocking the dispatcher?