have discovery rule (id: 23279) and graph prototypes in it.

Api call:
{
"jsonrpc":"2.0",
"method":"discoveryrule.get",
"params":

{ "itemids":[23279], "selectGraphs":"refer" }

,
"id":47,
"auth":"6bd880b1f963683fd908af4764bef817"
}

returns without graphs:
{
"jsonrpc": "2.0",
"result": [

{ "graphs": [], "itemid": "23279" }

],
"id": 47
}