title: How tensorflow reshape a tensor with dimension of None, like this [None,2,2,1]?
body: <p>The error is:</p>
  
  <blockquote>
    <p>TypeError: Failed to convert object of type  to Tensor. 
    Contents: [None, 4]. 
    Consider casting elements to a supported type.</p>
  </blockquote>
  
  <pre><code>import tensorflow as tf
  xs=tf.placeholder(tf.float32,[None,2,2,1],name='x-input')
  reshaped_xs=tf.reshape(xs,[None,4])
  
  with tf.Session() as sess:
      print sess.run(reshaped_xs)
  </code></pre>
  
  <p>The tensorflow version is: 1.4.0</p>
  
  <pre><code>docker run -d  --restart=always -p 8888:8888 tensorflow/tensorflow:1.4.0
  </code></pre>
  
  <p>So how to fix this? TKS!</p>