DMN13 — Unspecified conclusion

I remember discussions about allowing "-" in conclusions to mark an unspecified conclusion in a decision table. This would allow some of the conclusions in a multiple output decision table to be marked as "unspecified" where there was no output relevant for that conclusion for a specific rule and to allow rules in multi-hit tables to show that a particular combination of conditions had been considered but did not result in anything being added to the result set.
However the standard as written says that an output entry must adhere to the literal expression grammar, and '-' is not allowed. You have to return some FEEL value, e.g. 0, false, "N/A", null, etc.

RTF 1.3 is ending

Thank you for reporting the issue; it is likely valid but unfortunately the DMN 1.3 revision task force ran out of time before a member was able to resolve it. The issue will be deferred to the next revision task force.