title: NDB key.get() gives 'unicode' object has no attribute 'get' error
body: <p>I am migrating from db to ndb. There is a function to dynamically serve images in a path. In DB, i pass entity key(i.key()) as img_id and using db.get(key) I get the image. </p>
  
  <p>For NDB, i tried to pass key (i.key) and entity key(i.key.urlsafe()) to pass. But both these cases i get 'unicode' object has no attribute 'get' error.</p>
  
  <pre><code>**DB:**
  def get(self):
  image = db.get(self.request.get('img_id'))
  
  **HTML**
  &lt;a class="post-title" href ="{{permalink}}"&gt;{{i.content}}&lt;/a&gt;
  &lt;img src="/img?img_id={{i.key}}"&gt;&lt;/img&gt;
  
  **NDB**
  class ImageHandler(BlogHandler):
  def get(self):
      img=self.request.get('img_id')
      image=img.get()
      if image.image:
          self.response.headers['Content-Type'] = 'image/png'
          self.response.out.write(image.image)
      else:
          self.response.out.write('No image')     
  </code></pre>
  
  <p>I couldn't able find the mistake in this. Am i passing wrong type for key in key.get()?</p>