ConciseHash does not produce rdf:type shorthand when inside a blank node

[tpluscode]

See this snippet: https://runkit.com/embed/8weuxr2m8t3s

The concise hash includes a "a": [ ">https://code.described.at/EcmaScript" ], but the output has the full (or prefixed) rdf:type predicate where I expected [ a <https://code.described.at/EcmaScript> ]