UPDM — Ambiguos relation between Forecast and Milestone

From 8.6.12
"8.6.12.3 Description
A Forecast describes the actual or predicted status of a System at a Project Milestone - i.e., a point in the lifecycle of the
system. It can be a statement about the future state of one or more types of System or TechnicalStandardsForecast.
The Forecast is effective for a given timePeriod."

SystemGroup is also related to the Milestone (from 8.6.38).

There should be a constraint ensuring that there is at least one Milestone related to the SystemGroup directly and to the Forecast that is related to this SystemGroup. It would not make any sense to have a Forecast at the specific Milestone when a SystemGroup does not even exist.