'm' module load shows AttributeError: 'NoneType' object has no attribute 'rfind'

I'm new to pudb so please forgive noob errors.

Immediately on starting pudb , the 'm' key does show a list of modules, however none of mine are present. (presumably because they have not yet been imported?)
I'm guessing I need to load the module (via 'm') so I can set a breakpoint as I don't want to have to step all the way there.

I break after all the main's import statements are loaded (assuming that my module should be present in the list presented by 'm' now), I get this:

```
The program has terminated abnormally because of an exception.

A full traceback is below. You may recall this traceback at any time using the 'e' key. The debugger has entered post-mortem mode and will prevent further state changes.

Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/pudb/__init__.py", line 93, in runscript
dbg._runscript(mainpyfile)
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 444, in _runscript
self.run(statement, globals=globals_, locals=locals_)
File "/usr/lib/python2.7/bdb.py", line 400, in run
exec cmd in globals, locals
File "", line 1, in
File "/usr/bin/mlingestor-cli.py", line 16, in
from mlutil.sqs.util import get_queue, delete_message
File "/usr/bin/mlingestor-cli.py", line 16, in
from mlutil.sqs.util import get_queue, delete_message
File "/usr/lib/python2.7/bdb.py", line 49, in trace_dispatch
return self.dispatch_line(frame)
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 175, in dispatch_line
self.user_line(frame)
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 396, in user_line
self.interaction(frame)
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 364, in interaction
show_exc_dialog=show_exc_dialog)
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 2113, in call_with_ui
return f(*args, **kwargs)
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 2344, in interaction
self.event_loop()
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 2310, in event_loop
toplevel.keypress(self.size, k)
File "/usr/local/lib/python2.7/dist-packages/pudb/ui_tools.py", line 96, in keypress
result = self._w.keypress(size, key)
File "/usr/local/lib/python2.7/dist-packages/urwid/container.py", line 1128, in keypress
return self.body.keypress( (maxcol, remaining), key )
File "/usr/local/lib/python2.7/dist-packages/urwid/container.py", line 2269, in keypress
key = w.keypress((mc,) + size[1:], key)
File "/usr/local/lib/python2.7/dist-packages/urwid/container.py", line 1587, in keypress
key = self.focus.keypress(tsize, key)
File "/usr/local/lib/python2.7/dist-packages/pudb/ui_tools.py", line 101, in keypress
return handler(self, size, key)
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 1365, in pick_module
build_filtered_mod_list(filt_edit.get_edit_text()))
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 1329, in build_filtered_mod_list
for name, mod in list(sys.modules.items())
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 1330, in
if mod_exists(mod))
File "/usr/local/lib/python2.7/dist-packages/pudb/debugger.py", line 1311, in mod_exists
base, ext = splitext(filename)
File "/usr/lib/python2.7/posixpath.py", line 98, in splitext
return genericpath._splitext(p, sep, altsep, extsep)
File "/usr/lib/python2.7/genericpath.py", line 99, in _splitext
sepIndex = p.rfind(sep)
AttributeError: 'NoneType' object has no attribute 'rfind'
```

One thing that I'm doing that may be affecting this is that I have a
```
sys.path.extend(['src', 'mylibs/src'])
```
in my source to expand my PYTHONPATH. Is that not allowed with pudb?

The `mlutil` stuff in the stack frame is mine, however, as I mentioned, this shows up when I hit 'm' to load modules, not as part of runtime operation.