indexing on UUID() returns the wrong error

cbq.exe> create index i4 on default1(a,UUID()) where type="n1ql";
{
"requestID": "68a0e8d0-4a75-49fb-9af1-542a17460b6d",
"errors": [

{ "code": 3000, "msg": "Errors while parsing. - at )" }

],
"status": "fatal",
"metrics":

{ "elapsedTime": "1.4765ms", "executionTime": "1.3284ms", "resultCount": 0, "resultSize": 0, "errorCount": 1 }

}

expected: msg should say: "msg": "Expression not indexable: uuid() - at )"