title: Why does the None is getting appended in the list
body: <p>In the code below,I want the leaf elements from the dict.</p>
  
  <pre><code>group_children_map={'Mould': ['Yeast'], 'Living Organism': ['Animal', 'Plant', 'Mould'], 'Animal': ['Lion', 'Tiger', 'Cat', 'DOG'], 'Plant': ['Tulsi', 'Hibiscus', 'Aloe Vera']}
  print group_children_map
  node='Living Organism'
  leaf_list=[]
  def find_leaf(node):
      try_leaf=group_children_map.get(node)
      if try_leaf is None:
          #print node
          return node
      else:
          print try_leaf,"list"
          for l in try_leaf:
              #print l
              leaf_list.append(find_leaf(l))
  
  find_leaf(node)
  
  print leaf_list
  </code></pre>
  
  <p><strong>Expected output:</strong> </p>
  
  <pre><code>['Lion', 'Tiger', 'Cat', 'DOG', 'Tulsi', 'Hibiscus', 'Aloe Vera', 'Yeast']
  </code></pre>
  
  <p><strong>Actual result:</strong></p>
  
  <pre><code> ['Lion', 'Tiger', 'Cat', 'DOG', None, 'Tulsi', 'Hibiscus', 'Aloe Vera', None, 'Yeast', None]
  </code></pre>
  
  <p>why None is getting appended in the list...need help :/</p>