Property types should not expose the platform specific types used in the implementation. Instead, RO implementations should expose only platform independent types.
Example, from Isis RO viewer:
http://mmyco.co.uk:8180/isis-onlinedemo/restful/domain-types/TODO/properties/description
{
"rel" : "urn:org.restfulobjects:rels/return-type",
"href" : "http://mmyco.co.uk:8180/isis-onlinedemo/restful/domain-types/java.lang.String",
"method" : "GET",
"type" : "application/json;profile="urn:org.restfulobjects:repr-types/domain-type""
}