default Message newResponse(final Message parent, final Status st) {
        if (st == null) {
            return newResponse(parent, 0, "OK");
        }
        return newResponse(parent, st.getCode(), st.getErrorMsg());
    }
Creates a RPC response from status, return OK response
when status is null.

@param parent parent message
@param st     status with response
@return a response instance
jraft-core/src/main/java/com/alipay/sofa/jraft/rpc/RpcResponseFactory.java