Merge pull request #310 from bitstadium/fix/eliminate-potential-crash…

…-cause

Check if MetricsManager instance is actually initialized in sessionTr…

hockeysdk/src/main/java/net/hockeyapp/android/metrics/MetricsManager.java

@@ -6,7 +6,6 @@
 import android.os.AsyncTask;
 import android.os.Bundle;
 import android.text.TextUtils;
-import android.util.Log;
 
 import net.hockeyapp.android.Constants;
 import net.hockeyapp.android.PrivateEventManager;
@@ -283,7 +282,13 @@ private static void setUserMetricsEnabled(boolean enabled) {
      * @return YES if session tracking is enabled
      */
     public static boolean sessionTrackingEnabled() {
-        return isUserMetricsEnabled() && !instance.mSessionTrackingDisabled;
+        if (instance == null) {
+            HockeyLog.error(TAG, "MetricsManager hasn't been registered or User Metrics has been disabled. No User Metrics will be collected!");
+            return false;
+        }
+        else {
+            return isUserMetricsEnabled() && !instance.mSessionTrackingDisabled;
+        }
     }
 
     /**
@@ -468,7 +473,7 @@ public static void trackEvent(final String eventName, final Map<String, String>
             return;
         }
         if (instance == null) {
-            Log.w(TAG, "MetricsManager hasn't been registered or User Metrics has been disabled. No User Metrics will be collected!");
+            HockeyLog.error(TAG, "MetricsManager hasn't been registered or User Metrics has been disabled. No User Metrics will be collected!");
             return;
         }
         if (!isUserMetricsEnabled()) {