Save []byte with AQL?

I want save a dataset []byte() on ArangoDB with AQL. The saved object is "null".

query += `
            FOR d IN users
            FILTER (d._key == @Key)
            UPDATE d WITH { 
            TestData:{
                    test: @byte
            },
    } IN system_users`

    bindVars := map[string]interface{}{
        "byte":      mystruct.bytedata, //[]byte
        "key": 1234567,
        
    }

    cursor, err := arangodb.Db.Query(ctx, query, bindVars)

    if err != nil {
        fmt.Println(err)
    }

    defer cursor.Close()

If i use the none-aql function CreateDocument(), then is saved variable as binary []byte. What is the Problem in the BindVars?