NPE on FirebasePerfUrlConnection.instrument(FirebasePerfUrlConnection.java:13)

### Step 1: Describe your environment

* Android device: Galaxy J7,Grand Prime, S5
* Android OS version:android 6,5,7,9
* Google Play Services version: Not Known
* Firebase/Play Services SDK version: Not Known

### Step 2: Describe the problem:
Observing many crashes happening from Performance plugin in Firebase crashlytics console.

#### Steps to reproduce:
Not able to reproduce on testing device

#### Observed Results:

* Caused by java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Iterator

Crashlytics Logs

Fatal Exception: java.lang.ExceptionInInitializerError
at com.google.firebase.perf.internal.GaugeManager.(GaugeManager.java:5)
at com.google.firebase.perf.internal.GaugeManager.zzbf(GaugeManager.java:22)
at com.google.android.gms.internal.firebase-perf.zzat.(zzat.java:2)
at com.google.android.gms.internal.firebase-perf.zzat.zza(zzat.java:1)
at com.google.firebase.perf.network.FirebasePerfUrlConnection.instrument(FirebasePerfUrlConnection.java:13)
at com.adobe.mobile.RequestHandler.requestConnect(RequestHandler.java:390)
at com.adobe.mobile.RequestHandler.retrieveAnalyticsRequestData(RequestHandler.java:246)
at com.adobe.mobile.AnalyticsWorker$1.run(AnalyticsWorker.java:304)
at java.lang.Thread.run(Thread.java:818)

-----------------------------------

java.util.List.iterator()' on a null object reference
at com.google.firebase.perf.internal.zzp.(zzp.java:16)
at com.google.firebase.perf.internal.zzp.(zzp.java:6)
at com.google.firebase.perf.internal.zzp.(zzp.java:47)
at com.google.firebase.perf.internal.GaugeManager.(GaugeManager.java:5)
at com.google.firebase.perf.internal.GaugeManager.zzbf(GaugeManager.java:22)
at com.google.android.gms.internal.firebase-perf.zzat.(zzat.java:2)
at com.google.android.gms.internal.firebase-perf.zzat.zza(zzat.java:1)
at com.google.firebase.perf.network.FirebasePerfUrlConnection.instrument(FirebasePerfUrlConnection.java:13)
at com.adobe.mobile.RequestHandler.requestConnect(RequestHandler.java:390)
at com.adobe.mobile.RequestHandler.retrieveAnalyticsRequestData(RequestHandler.java:246)
at com.adobe.mobile.AnalyticsWorker$1.run(AnalyticsWorker.java:304)
at java.lang.Thread.run(Thread.java:818)

#### Expected Results:

* Should not crash

#### Relevant Code:

```
apply plugin: 'com.google.firebase.firebase-perf'
implementation "com.google.firebase:firebase-perf:16.2.2"
classpath "com.google.firebase:firebase-plugins:1.1.5"

```

Inizia con lo stack trace segnalato in FirebasePerfUrlConnection.instrument, quindi ispeziona il percorso di inizializzazione attraverso GaugeManager e zzp usando firebase-perf 16.2.2. Prova a riprodurre il crash nell’ambiente Android descritto, incluso il percorso delle chiamate di Adobe RequestHandler. Il lavoro è completato quando è stata identificata una riproduzione affidabile e ci si è assicurati che la richiesta non vada più in crash a causa dell’iteratore null.

Scritto dal modello di indicizzazione a partire dal testo della issue.