Invalid JSON-LD syntax; "@reverse" value must be an object.

[coret]

#1795 added the @reverse property to the JSON-LD API. But, when an object doesn't have subjectValuesForReverse() the resulting JSON-LD will have @reverse: [] making the JSON-LD invalid.

I ran into this issue when processing the API's JSON-LD with https://json-ld.org/playground/ and https://www.easyrdf.org/converter. According to https://json-ld.org/spec/latest/json-ld/:

If the node object contains the @reverse key, its value MUST be a JSON object containing members representing reverse properties. Each value of such a reverse property MUST be an absolute IRI, a relative IRI, a compact IRI, a blank node identifier, a node object or an array containing a combination of these.

A possible fix would be to change

omeka-s/application/src/Api/Representation/AbstractResourceEntityRepresentation.php

Line 123 in d167dde

['@reverse' => $this->subjectValuesForReverse()]

into (count($reverse)>0?['@reverse' =>$reverse]:null)

where $reverse=$this->subjectValuesForReverse(); is added before

omeka-s/application/src/Api/Representation/AbstractResourceEntityRepresentation.php

Line 110 in d167dde

return array_merge(

[zerocrates]

Thanks for the report: we'll look into it, either removing the key or making it be an empty object rather than an empty array.

[zerocrates]

The fix here is released, as part of version 3.2.1.