Tensorflow retrain.py Image directory not found error

[admin]

I am trying out Tensorflow for Poets from <a href="https://datanonymous.wordpress.com/image-classification-using-tensorflow/" rel="nofollow noreferrer">here</a> which retrains the last later of Inception on Ubuntu 14.04 CPU

following the guide I ran this code

    python tensorflow/examples/image_retraining/retrain.py \
–bottleneck_dir=tf_files/bottlenecks \
–how_many_training_steps 500 \
–model_dir=tf_files/inception \
–output_graph=tf_files/retrained_graph.pb \
–output_labels=tf_files/retrained_labels.txt \
–image_dir=tf_files/flower_photos

and I got the following error

Image directory '' not found.
Traceback (most recent call last):
  File "tensorflow/examples/image_retraining/retrain.py", line 774, in <module>
    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 671, in main
    class_count = len(image_lists.keys())
AttributeError: 'NoneType' object has no attribute 'keys

Knowing this issue relates to where my images are stored, I have them placed in the home folder which applies correctly to the last command

image_dir=tf_files/flower_photos

So now my question is why am I getting this error even though the image directory is correct?