E....

======================================================================

ERROR: test_empties (tester.ProblemTests)

----------------------------------------------------------------------

Traceback (most recent call last):

  File ".../test.py", line 39, in test_empties

    self.assertNoOrder([], tags_by_band('My Jolly Band'))

  File ".../test.py", line 35, in assertNoOrder

    self.assertEqual(set(first), set(second))

TypeError: 'NoneType' object is not iterable



----------------------------------------------------------------------

Ran 5 tests in 0.002s



FAILED (errors=1)