code: def testStratifiedSamplingFromEmptyTree(self):
      with self.assertRaises(
          Exception, msg="Cannot sample from an empty sum tree."
      ):
          self._tree.stratified_sample(5)
  
imports: import random
  import unittest
  from reagent.replay_memory import sum_tree
label_desc: Use image node_id 14 for calling the SumTreeTest obj's underlying member method code with example usage: obj.testStratifiedSamplingFromEmptyTree() without return types