Which folder should my file "vgg_16.ckpt" be placed in?

[RishengZhou]

My error report :

_**INFO:tensorflow:Error reported to Coordinator: <class 'ValueError'>, Can't load save_path when it is None.
Traceback (most recent call last):
File "D:/ssd_tensorflow_LevinJ/train_model.py", line 435, in
obj.run()
File "D:/ssd_tensorflow_LevinJ/train_model.py", line 429, in run
self.__start_training()
File "D:/ssd_tensorflow_LevinJ/train_model.py", line 223, in __start_training
save_interval_secs=self.save_interval_secs)
File "D:\FaceDlib\lib\site-packages\tensorflow\contrib\slim\python\slim\learning.py", line 748, in train
master, start_standard_services=False, config=session_config) as sess:
File "D:\FaceDlib\lib\contextlib.py", line 81, in enter
return next(self.gen)
File "D:\FaceDlib\lib\site-packages\tensorflow\python\training\supervisor.py", line 1004, in managed_session
self.stop(close_summary_writer=close_summary_writer)
File "D:\FaceDlib\lib\site-packages\tensorflow\python\training\supervisor.py", line 832, in stop
ignore_live_threads=ignore_live_threads)
File "D:\FaceDlib\lib\site-packages\tensorflow\python\training\coordinator.py", line 389, in join
six.reraise(*self._exc_info_to_raise)
File "D:\FaceDlib\lib\site-packages\six.py", line 693, in reraise
raise value
File "D:\FaceDlib\lib\site-packages\tensorflow\python\training\supervisor.py", line 993, in managed_session
start_standard_services=start_standard_services)
File "D:\FaceDlib\lib\site-packages\tensorflow\python\training\supervisor.py", line 730, in prepare_or_wait_for_session
init_feed_dict=self._init_feed_dict, init_fn=self._init_fn)
File "D:\FaceDlib\lib\site-packages\tensorflow\python\training\session_manager.py", line 296, in prepare_session
init_fn(sess)
File "D:\FaceDlib\lib\site-packages\tensorflow\contrib\framework\python\ops\variables.py", line 750, in callback
saver.restore(session, model_path)
File "D:\FaceDlib\lib\site-packages\tensorflow\python\training\saver.py", line 1534, in restore
raise ValueError("Can't load save_path when it is None.")
ValueError: Can't load save_path when it is None.
ERROR:tensorflow:==================================
Object was never used (type <class 'tensorflow.python.framework.ops.Tensor'>):
<tf.Tensor 'init_ops/report_uninitialized_variables/boolean_mask/GatherV2:0' shape=(?,) dtype=string>
If you want to mark it as used call its "mark_used()" method.
It was originally created here:
File "D:/ssd_tensorflow_LevinJ/train_model.py", line 435, in
obj.run() File "D:/ssd_tensorflow_LevinJ/train_model.py", line 429, in run
self.__start_training() File "D:/ssd_tensorflow_LevinJ/train_model.py", line 223, in __start_training
save_interval_secs=self.save_interval_secs) File "D:\FaceDlib\lib\site-packages\tensorflow\contrib\slim\python\slim\learning.py", line 791, in train
should_retry = True File "D:\FaceDlib\lib\site-packages\tensorflow\python\util\tf_should_use.py", line 189, in wrapped
return add_should_use_warning(fn(*args, kwargs))
==================================

which folder should my file "vgg_16.ckpt" be placed in ?
train_dir or checkpoint_path ???