Rudder

This hardcoded in CFEngine, and even CFEngine core team knows how to correct that.

We can't prevent it from Rudder because we don't know (and can't know) statically what are the defined variables (most are defined during run).

Moreover, there's several cases: the hardest case is when the variable is not defined in a promiser, because in such a case, the iteration engine just don't have the missing iteration. Somewhere in the code, there's a part that wait for variable definition to add in the iteration list, and that never happens.

So we may not be able to even log for that.

Some subcase may perhaps be endled. For example, in templates (enforce a file content), when for ex ${sys. the ipv6 interface} is empty, we may be able to not skip it.