Edifact - Can UNG/UNE block be empty (contain zero messages)?

Question

In the EDIFACT structure you can use UNG/UNE segments to group a set of messages functionally inside an interchange (UNB/UNZ segments). The functional groupings can be used to provide an extra layer of semantics over a collection of messages.

My question is whether it is allowed to output a functional group without any messages inside it (as opposed to not outputting the UNG/UNE segments at all)?

I have tried looking over the internet on this issue but I have yet to find any clarification on this specific point.

To add some context, my scenario is an interchange with four types of messages grouped functionally. One of these groups contains a message for each underlying item in the database. If the database has no records, then no messages will be output for that group. In this case the group will be empty. Do you create an empty UNG/UNE block or do you not create the block at all? (the other three groups will always be populated)

I am really looking for some citeable source to support an answer either way.

Answer 1

within UNG/UNE messages are mandatory (UNH-UNT).
just like empty interchanges (UNB-UNZ) are not allowed.

Source: ISO 9735-2:2002; see http://www.gefeg.com/jswg/v41/data/v41_docs.htm

btw, UNG/UNE is not often used....

Your way of looking at envelopes is somewhat funny. You have messages that need to be enveloped (or grouped, and than enveloped). One does not first make the envelopes, and than wait if they get filled up ;-))
(at least, that is how I deal with snail mail, and for edifact the same logic is used)