message: tfdbg: fix a bug in the example debug_tflearn_iris
  Previously, if neither the --debug or --tensorboard_debug_address flag is used, the example will error out because the variable debug_hook is unset.
diff: @@ -113,17 +113,16 @@ def main(_):
  n_classes=3,
  model_dir=model_dir)
  - hooks = None
  if FLAGS.debug and FLAGS.tensorboard_debug_address:
  raise ValueError(
  "The --debug and --tensorboard_debug_address flags are mutually "
  "exclusive.")
  + hooks = []
  if FLAGS.debug:
  - debug_hook = tf_debug.LocalCLIDebugHook(ui_type=FLAGS.ui_type,
  - dump_root=FLAGS.dump_root)
  + hooks.append(tf_debug.LocalCLIDebugHook(ui_type=FLAGS.ui_type,
  + dump_root=FLAGS.dump_root))
  elif FLAGS.tensorboard_debug_address:
  - debug_hook = tf_debug.TensorBoardDebugHook(FLAGS.tensorboard_debug_address)
  - hooks = [debug_hook]
  + hooks.append(tf_debug.TensorBoardDebugHook(FLAGS.tensorboard_debug_address))
  # Train model, using tfdbg hook.
  classifier.train(training_input_fn,
  