JSONRPC 2.0 compatibility fix: result in response can be null
JSONRPC 2.0 compatibility fix: result in response can be null (Tests)
JSONRPC 2.0 compatibility fix: result in response can be null (+BatchRequestTest)
Merge pull request #8 from d-ulyanov/response-json-rpc-2-fix

JSONRPC 2.0 compatibility fix: result in response can be null

Thanks @d-ulyanov :+1: