Do not emit null fields or replace them with empty strings

[mterron]

Currently the json filter emits fields set to null. It is difficult to manipulate this fields downstream.

I'd like to see an option to either do not emit this fields at all (eg, if field1 => null remove field1) or replace the null with an empty string (eg if field1 => null then field1 => "").

[kunisen]

Any update here?