Couchbase view using multiple keys to get result

Couchbase Server
1

I have the following document

{
   "Credit_Amount": 99,
   "Acc_no": 138,
   "Job_No": "esmwga",
   "Source_No": "x",
   "Temp": 1017,
   "Document_No": "gaf",
   "Debit_Amount": 67,
   "User_Id": "xirbzsewiw"
}

and my map function is this

function (doc, meta) {
    if(doc.Type == "GLEntry")
    {
          emit([doc.Acc_no,doc.User_Id],[doc.Credit_Amount,doc.Debit_Amount]);
    }
}

and this is my reduce function

function(key,values,rereduce){
    var sum1=0,sum2=0;
    for(var i=0;i<values.length;++i)
    {
        sum1+=values[i][0];
        sum2+=values[i][1];
    }
return ([sum1,sum2])
}

when I pass this key

[138,"xirbzsewiw"]
group level 2

I get this output

[ 99, 67 ]

But When I give this as key

[138]
group level 1

I get empty result. But what I have understood is it will group using only acc number when I give group level 1 so it should give same output. Am I doing something wrong?