Writing to Json Output produce file that is not proper Json. During validation generate error:

Code:
Error: Parse error on line 1:
...replacement":null}]}{"data":[{"producer"
-----------------------^
Expecting 'EOF', '}', ',', ']', got '{'
This Joson does not looke like... Json. First of all for some weired reason this step produces as many Json as no of input rows ("append" option must be on or I will get just one row). I want sone combined Json.

Any way to have valid Json?
Regards