Hello, dubbo team. I'm learning the dubbo project , and I found some problems with rpc.merger module
listed as below:

1, The ArrayMerger uses its first element's component type to create a new Array. But some times
if we use

        class Person{};
        class Teacher extends Person{};
        Person[] a= {new Person()};
        Teacher[] b= {new Teacher()};
        Object[] result = ArrayMerger.INSTANCE.merge(a,b);

This will fail with "array element type mismatch"

2, The ArrayMerger doesn't allow null object , but ListMerger and MapMerger allows user to input
null object

       MergerFactory.getMerger(List.class).merge(list1, list2, null);

this is not semantic consistent

3, All the mergers doesn't check for null input and MergeFactory.getmerger could return null
if the request class not in cache.