<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _build_send_args(self, **kwargs):
 """Merge optional arguments with defaults. :param kwargs: Keyword arguments to `Session::send` """

        out = {}
        out.update(self._default_send_args)
        out.update(kwargs)
        return out