Empty args will omit kwargs on some message types

[Eric Chapman]

The code for additional fields is skipping kwargs if args is 'nil' or 'empty'. See below

        return payload if (self.arguments.nil? or self.arguments.empty?)
        payload.push(self.arguments)

        return payload if (self.argumentskw.nil? or self.argumentskw.empty?)
        payload.push(self.argumentskw)