[afonsojanu]

Fixes the crash reported in #646.

Job.__repr__ tries to drop the trailing s from the unit name for singular jobs (self.unit[:-1] if self.interval == 1 else self.unit), but a Job doesn't get a unit until one of the time-unit properties (.minute, .day, ...) or .do() sets it. Since every() defaults interval to 1, repr(schedule.every()) slices None and blows up with TypeError: 'NoneType' object is not subscriptable. This can bite you in an interactive session or any debug logging that reprs a job before it's fully composed.

There's actually already a test for exactly this "partially-composed job" scenario (test_to_repr's schedule.every(10) case), but it only happens to dodge the bug because interval=10 takes the other branch of that conditional and never slices anything.

Fix: route both places that do this slicing through a small format_unit helper that passes None straight through, and add a case to that same test for the default interval of 1, which is the one that actually crashed.

>>> import schedule
>>> repr(schedule.every())
Traceback (most recent call last):
  ...
TypeError: 'NoneType' object is not subscriptable

now returns 'Every 1 None do [None] (last run: [never], next run: [never])' instead, matching what the interval>1 case already does.