Note that documentToPojo takes a Class as its second argument. any(Foo.class) returns an argument of type Foo, not of type Class<Foo>, whereas eq(WorkItemDTO.class) should return a Class<WorkItemDTO> as expected. I’d do it this way:
when(mongoUtil.documentToPojo(
Mockito.any(Document.class),
Mockito.eq(WorkItemDTO.class))).thenReturn(...);