input: def dropLeafNodes(head):
      """Drop all the leaf nodes from the given Huffman tree.
      >>> dropLeafNodes({})
      WARNING: This test case is missing or invalid. Please provide the head of the Huffman tree in dict format for testing. Example: dropLeafNodes({'left': {'left': None, 'right': None}, 'right': {'left': None, 'right': None}})
      """
      if head and not head.left and not head.right:
          return None
  
      if not head:
          return None
  
      head.left = dropLeafNodes(head.left)
      head.right = dropLeafNodes(head.right)
  
      return head
output:     if head and not head.left and not head.right:
          return None
  
      if not head:
          return None
  
      head.left = dropLeafNodes(head.left)
      head.right = dropLeafNodes(head.right)
  
      return head