public void someMethod() throws Exception {
        // null
        when(request.getParameter("abc")).thenReturn(null);

        try {
            abc.manageIncome(request, response, nancy, null);
            fail();
        } catch(IllegalArgumentException ex) {}

        verify(nancy.manageIncome(request, response, nancy, "abc"));
    }

/* BAD */  verify(nancy.manageIncome(request, response, nancy, "abc"));
/* GOOD */ verify(nancy).manageIncome(request, response, nancy, "abc");