title: Firebase neither give callback nor error
body: <p>I am retrieving data from firebase database.</p>
  
  <p>When I debug the code from simulator it gives all the data from that node but when i debug the code from device it neither goes to success block nor error block. Nothing happens.</p>
  
  <p>Code I have written is given below.</p>
  
  <pre><code>FIRDatabase.database().reference().child("registeredUserEmail").observeSingleEventOfType(.Value, withBlock: { (snapshot) in
          debugPrint(snapshot.value)
          if snapshot.hasChild(email.escapeEmail()) {
              debugPrint("false")
              completion(false)
          }
          else {
              debugPrint("true")
              completion(true)
          }
      }) { (error) in
          debugPrint("error in isEmailFree - " + error.localizedDescription)
          completion(false)
      }
  </code></pre>
  
  <p>Here are the console logs when app first time launches</p>
  
  <p>2016-06-07 11:36:30.471[4067:1092564] Configuring the default app.
  2016-06-07 11:36:30.530[4067:]  Firebase Analytics v.3200000 started
  2016-06-07 11:36:30.532 Artup[4067:]  To enable debug logging set the following application argument: -FIRAnalyticsDebugEnabled 
  2016-06-07 11:36:30.576[4067:1092564] Firebase Crash Reporting: Successfully enabled
  2016-06-07 11:36:30.590:  FIRInstanceID AppDelegate proxy enabled, will swizzle app delegate remote notification handlers. To disable add "FirebaseAppDelegateProxyEnabled" to your Info.plist and set it to NO
  2016-06-07 11:36:30.659 Artup[4067:]  Successfully created Firebase Analytics App Delegate Proxy automatically. To disable the proxy, set the flag FirebaseAppDelegateProxyEnabled to NO in the Info.plist
  Config not fetched
  Error Error Domain=com.google.remoteconfig.ErrorDomain Code=8002 "(null)" UserInfo={error_throttled_end_time_seconds=1465279698.4105051}
  2016-06-07 11:36:31.450 Artup[4067:]  Firebase Analytics enabled</p>