DeltaCode not handling copyright holders properly

I am doing a delta between a scan created by ScanCode version 2.9.7.post1.81f177e and another scan created by ScanCode version 3.0.2.post1270.ac0e1e184. I am encountering the following error:
```
Traceback (most recent call last):
File "/home/jono/nexb/src/deltacode/bin/deltacode", line 11, in
load_entry_point('deltacode', 'console_scripts', 'deltacode')()
File "/home/jono/nexb/src/deltacode/local/lib/python2.7/site-packages/click/core.py", line 722, in __call__
return self.main(*args, **kwargs)
File "/home/jono/nexb/src/deltacode/local/lib/python2.7/site-packages/click/core.py", line 697, in main
rv = self.invoke(ctx)
File "/home/jono/nexb/src/deltacode/local/lib/python2.7/site-packages/click/core.py", line 895, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/home/jono/nexb/src/deltacode/local/lib/python2.7/site-packages/click/core.py", line 535, in invoke
return callback(*args, **kwargs)
File "/home/jono/nexb/src/deltacode/src/deltacode/cli.py", line 90, in cli
deltacode = DeltaCode(new, old, options)
File "/home/jono/nexb/src/deltacode/src/deltacode/__init__.py", line 61, in __init__
self.copyright_diff()
File "/home/jono/nexb/src/deltacode/src/deltacode/__init__.py", line 227, in copyright_diff
utils.update_from_copyright_info(delta)
File "/home/jono/nexb/src/deltacode/src/deltacode/utils.py", line 127, in update_from_copyright_info
update_modified_from_copyright_info(delta)
File "/home/jono/nexb/src/deltacode/src/deltacode/utils.py", line 160, in update_modified_from_copyright_info
new_holders = set(holder for copyright in new_copyrights for holder in copyright.holders)
File "/home/jono/nexb/src/deltacode/src/deltacode/utils.py", line 160, in
new_holders = set(holder for copyright in new_copyrights for holder in copyright.holders)
TypeError: 'NoneType' object is not iterable
```