Reduce function Null checks

[Jeyhun Karimov]

Hi community,

When using, reduce(Reducer,Reducer, KeyValueMapper,String) function in
KTable, the NullPointerExeption is thrown. In specified function, below
call is made:

        return reduce(adder, subtractor, selector, null, null, name);

and afterwards, in reduce(Reducer,Reducer,
KeyValueMapper,Serde,Serde,String) function, the exception is thrown while
creating ChangedSerializer. I think null checks should be added to escape
the exception.

Jeyhun
-- 
-Cheers

Jeyhun