Empty facet list is returned in JSON response of Featured Search

When accept header is set to "application/json", an empty list is returned for facets in Feature Search although there is no problem with "text/html".

Although some facets exist, there is not any facet in result for the following command:

curl -i -H "Accept:application/json" "http://localhost:8080/contenthub/contenthub/search/featured?queryTerm=paris"

response:
{
"documents": [

{ "localid": "urn:content-item-sha1-d8cb233824c493e80d744a8120469e40be97444d", "mimetype": "text\/plain", "title": "paris", "enhancementcount": 4 }

],
"facets": [],
"relatedkeywords": [

{"paris": []}

]
}