title: CRITICAL: tensorflow:Category has no images - validation
body: <p>I'm trying to retraining the Inception v3 model in tensorflow for my own custom categories. I have downloaded some data and formatted it into directories. When I run, the python script creates bottlenecks for the images, and then when it runs, on the first training step( step 0) it has a critical error, where it tries to modulo by 0.  It appears in the get_image_path function when computing the mod_index, which is index % len(category_list) so the category_list must be 0 right?</p>
  
  <p>Why is this happening and how can I prevent it?</p>
  
  <p>EDIT: Here's the exact code I'm seeing inside docker</p>
  
  <pre><code>2016-07-04 01:27:52.005912: Step 0: Train accuracy = 40.0%
  2016-07-04 01:27:52.006025: Step 0: Cross entropy = 1.109777
  CRITICAL:tensorflow:Category has no images - validation.
  Traceback (most recent call last):
    File "tensorflow/examples/image_retraining/retrain.py", line 824, in &lt;module&gt;
      tf.app.run()
    File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/platform/app.py", line 30, in run
      sys.exit(main(sys.argv))
    File "tensorflow/examples/image_retraining/retrain.py", line 794, in main
      bottleneck_tensor))
    File "tensorflow/examples/image_retraining/retrain.py", line 484, in get_random_cached_bottlenecks
      bottleneck_tensor)
    File "tensorflow/examples/image_retraining/retrain.py", line 392, in get_or_create_bottleneck
      bottleneck_dir, category)
    File "tensorflow/examples/image_retraining/retrain.py", line 281, in get_bottleneck_path
      category) + '.txt'
    File "tensorflow/examples/image_retraining/retrain.py", line 257, in get_image_path
      mod_index = index % len(category_list)
  ZeroDivisionError: integer division or modulo by zero
  </code></pre>