pass complex object in objective c using suez

Question

I am using sudzc to communicate to the WCF Service. The method expects a complex object("Category") and processes the request.The code for calling the service is:

SDZiPadDocSyncService *service = [SDZiPadDocSyncService service];
SDZCategory *cat = [[SDZCategory alloc]init];
cat.categoryId = (int) catId;
[service getDocsByCatId:self action:@selector(getDocsByCatIdHandler:) category:cat]; 

The code for the handler is:

- (void) getDocsByCatIdHandler: (id) value {
        NSLog(@"value=%@",value);
        NSMutableArray* result = (NSMutableArray*)value;
    NSLog(@"getDocsByCatId returned the value: %@", result);     
    }

Both the "NSLog"(value & result) return a blank result,i.e.there isn't any data in it.Do I have to call the method differently?

EDIT:- I am initializing "catId" in a previous line.So,catId isn't blank.