def svn_txdelta_apply(source, target, result_digest, pool):
    handler = ctypes.POINTER(core.svn_txdelta_window_handler_t(0))
    handler_baton = ctypes.POINTER(ctypes.c_void_p)
    error_info = ctypes.c_char_p(0)
    core.svn_txdelta_apply(types.Stream(source), types.Stream(target),
                           result_digest, error_info, pool,
                           handler, handler_baton)
    return handler, handler_baton


---
  File "/Users/Augie/ctypes-branch/hg_delta_editor.py", line 593, in apply_textdelta
    pool)
  File "/Users/Augie/ctypes-branch/svnwrap/svn_ctypes_wrapper.py", line 21, in svn_txdelta_apply
    handler = ctypes.POINTER(core.svn_txdelta_window_handler_t(0))
SystemError: NULL result without error in PyObject_Call