ADDL workbench ADL serialized produces invalid ADL with prohibited attributes without matches {...} block

To reproduce: Open the two attached archetypes in the ADL workbench. Then open the serialized form of the protocol_prohibited archetype. The definition reads:

definition
OBSERVATION[id1.1] matches { – observation
protocol existence matches {0} matches {
}
}

Which is not valid ADL2 because matches {} needs content between the { and } characters.
This is the flat output, the differential version has an extra '/' but has the same problem in the output.