billing: Refactor renewal_amount to return 0 instead of None.

corporate/lib/stripe.py

@@ -110,12 +110,12 @@ def next_invoice_date(plan: CustomerPlan) -> datetime:
         periods += 1
     return dt
 
-def renewal_amount(plan: CustomerPlan, event_time: datetime) -> Optional[int]:  # nocoverage: TODO
+def renewal_amount(plan: CustomerPlan, event_time: datetime) -> int:  # nocoverage: TODO
     if plan.fixed_price is not None:
         return plan.fixed_price
     last_ledger_entry = add_plan_renewal_to_license_ledger_if_needed(plan, event_time)
     if last_ledger_entry.licenses_at_next_renewal is None:
-        return None
+        return 0
     assert(plan.price_per_license is not None)  # for mypy
     return plan.price_per_license * last_ledger_entry.licenses_at_next_renewal
 
@@ -473,7 +473,7 @@ def estimate_annual_recurring_revenue_by_realm() -> Dict[str, int]:  # nocoverag
             status=CustomerPlan.ACTIVE).select_related('customer__realm'):
         # TODO: figure out what to do for plans that don't automatically
         # renew, but which probably will renew
-        renewal_cents = renewal_amount(plan, timezone_now()) or 0
+        renewal_cents = renewal_amount(plan, timezone_now())
         if plan.billing_schedule == CustomerPlan.MONTHLY:
             renewal_cents *= 12
         # TODO: Decimal stuff

corporate/views.py

@@ -174,9 +174,6 @@ def billing_home(request: HttpRequest) -> HttpResponse:
         # Should do this in javascript, using the user's timezone
         renewal_date = '{dt:%B} {dt.day}, {dt.year}'.format(dt=start_of_next_billing_cycle(plan, now))
         renewal_cents = renewal_amount(plan, now)
-        # TODO: this is the case where the plan doesn't automatically renew
-        if renewal_cents is None:  # nocoverage
-            renewal_cents = 0
         charge_automatically = plan.charge_automatically
         if charge_automatically:
             payment_method = payment_method_string(stripe_customer)