TypeError When Scoring Decaying Map Challenge

[sentry]

Sentry Issue: BACKEND-4D

TypeError: unsupported operand type(s) for -: 'int' and 'str'
(9 additional frame(s) were not displayed)
...
  File "backend/exception_handler.py", line 50, in handle_exception
    raise exc
  File "rest_framework/views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "challenge/views.py", line 309, in post
    solve = challenge.points_plugin.score(user, team, flag, solve_set.filter(correct=True))
  File "plugins/points/base.py", line 29, in score
    points = self.get_points(team, flag, solves.count())
  File "plugins/points/decay.py", line 17, in get_points
    return int(round(min_points + ((challenge.score - min_points) * (decay_constant ** max(solves - 1, 0)))))

[thebeanogamer]

When the user submits a change to the flag metadata (for example changing the radius of a map challenge), the min_points and decay_constant fields are getting written as empty string rather than the expected behavior of them being excluded.

 'flag_metadata': {'radius': 1,
  'location': [0, 0],
  'min_points': '',
  'decay_constant': ''},

That means that these lines collect empty string, causing the type error

core/src/plugins/points/decay.py

Lines 15 to 16 in aef1c79

	decay_constant = challenge.flag_metadata.get("decay_constant", 0.99)
	min_points = challenge.flag_metadata.get("min_points", 100)

Either we need to make these ignore empty string, or not make those fields get written unnecessarily (or move this out of flag_metadata).

[jchristgit]

not make those fields get written unnecessarily

I'm a fan of this approach personally, then if we later add other parts we don't need to adjust there