title: Attribute is not defined in Gatling
body: <p>I have this simulation file.
  My idea is created a json file, in the json file has some parameter.
  The parameters will be passed value by feeder in gatling.
  But the problem is when I do that, parameter is not passed value.</p>
  
  <pre><code>package tci3accountPro
  
  import baseConfig.BaseSimulation
  import io.gatling.core.Predef._
  import io.gatling.http.Predef._
  import tci3accountPro.models.bodyRegisterSubs
  import core.api.ApiUtil
  
  import scala.concurrent.duration._
  
  class registerSubscriptions extends BaseSimulation{
  
    val username = "105C169260"
  
    val cashAccount = "11111"
  
    val proCode = "IWEALTH_PRO"
    val typeText = "TRIAL"
    val referrerId105C = "105C310885"
  
    var ini = new GetTokenApi
  
    val token = ini.getToken(username)
  
    val registerSubs = http.baseUrl(accountProDomain + accountProSubs)
      .header("Authorization", token)
      .header("Content-Type","application/json")
  
  
    var feeder =  Iterator.continually(Map(
      "cashAccount" -&gt; cashAccount,
      "code105C" -&gt; username,
      "proCode" -&gt; proCode,
      "type" -&gt; typeText,
      "referrerId105C" -&gt; referrerId105C
    ))
  
    def registerSub() = {
      feed(feeder)
      exec(http("register Subscriptions")
        .post("")
        .body(ElFileBody("bodies/bodyRegisterSubs.json")).asJson
        .check(status.is(200)))
    }
  
    val scn = scenario("register Subscriptions")
      .exec(registerSub)
  
    setUp(scn.inject(atOnceUsers(1),rampUsersPerSec(1) to 5 during (10 seconds)).protocols(registerSubs)).maxDuration(1 minutes)
      .assertions(global.responseTime.max.lt(2000), global.successfulRequests.percent.gt(95))
  }
  </code></pre>
  
  <p>and the json file    </p>
  
  <pre><code>{
    "cashAccount": "${cashAccount}",
  "code105C": "${code105C}",
  "proCode": "${proCode}",
  "type": "${type}",
  "referrerId105C": "${referrerId105C}"
  }
  </code></pre>
  
  <p>But when run the simulation, it shows : no attribute name "cashAccount" is defined.
  Can someone help?</p>