Is there a XLAT IF(..) like expansion?

Hello again I'm trying to accomplish the following (pseudo code): In rlm_rest module config: authenticate { body = "json" data = '{ "token" : "xxxxxxx", "states": [ "x", "y" ], "resourceIds: PSEUDO_CODE>> IF(%{control:Cust-Resource-Uuid}, [ "%{control:Cust-Resource-Uuid}" ], null) <<PSEUDO_CODE , }' } I.e. when the custom attribute is set, the JSON's "resourcesIds" property should be an array containing the attribute's string content, otherwise "null". Your help is much appreciated! Cheers, Till