First of all, this issue was introduced by fix for JSONRPC-28 which in fact did right thing, but also allows exception to propagate that was previously transformed to Future (in JsonRpcTx):

try { 
    rootJson = jsonConverter.fromBus(path, omshard.read(store2str(store2int(store)), peer.getName(), arg.getPath())); 
} catch (Exception e) { 
  return readFailure(e); 
}

Immediate fix it put this logic back, but also another bigger task that is to extend (or create in first place) CSIT suite to exercise CRUD operations on "test service". This has to include various YANG constructs (list in container, container as list item, etc ...) to ensure all data operations are handled correctly.