Example 19 from examples.py ends with "AttributeError: next_update" #60

Running: Example 19
Traceback (most recent call last):
File "examples.py", line 210, in
for example in examples: example()
File "examples.py", line 20, in wrapped
fn()
File "examples.py", line 204, in example19
for i in pbar([]):
File "/usr/lib/python2.7/dist-packages/progressbar/init.py", line 184, in next
self.finish()
File "/usr/lib/python2.7/dist-packages/progressbar/init.py", line 321, in finish
self.update(self.maxval)
File "/usr/lib/python2.7/dist-packages/progressbar/init.py", line 276, in update
if not self._need_update(): return
File "/usr/lib/python2.7/dist-packages/progressbar/init.py", line 251, in _need_update
if self.currval >= self.next_update or self.finished: return True
AttributeError: next_update