Invoicing of free recurring plans trigger a double billing detection

[pierre]

Because $0 recurring items aren't repaired, after a change plan, we end up with two ADD items on the same interval (see

killbill/invoice/src/main/java/org/killbill/billing/invoice/tree/ItemsInterval.java

Line 222 in 4320ce9

Preconditions.checkState(addItems.size() <= 1, "Double billing detected: %s", items);

).

[pierre]

Depending on the scenario, a repair check of $0 can be triggered too (see

killbill/invoice/src/main/java/org/killbill/billing/invoice/tree/Item.java

Line 149 in 4320ce9

Preconditions.checkState(increment.compareTo(BigDecimal.ZERO) > 0, "Invalid repair increment='%s', item=%s", increment, this);

).