"[Python] #2907 Fix returning null from functions with output
            parameters.  Ensures OUTPUT and INOUT typemaps are handled
            consistently wrt return type.

            New declaration of SWIG_Python_AppendOutput is now:

              SWIG_Python_AppendOutput(PyObject* result, PyObject* obj, int is_void);

            The 3rd parameter is new and the new $isvoid special variable
            should be passed to it, indicating whether or not the wrapped
            function returns void.

            Also consider replacing with:

              SWIG_AppendOutput(PyObject* result, PyObject* obj);

            which calls SWIG_Python_AppendOutput with same parameters but adding $isvoid
            for final parameter."