Add null check to NavigationModeFeatureFlag

Test: none
Fixes: 185790043
Change-Id: I591c18df0394e7ab4286687fffe8713a4507373e
diff --git a/quickstep/src/com/android/quickstep/util/NavigationModeFeatureFlag.java b/quickstep/src/com/android/quickstep/util/NavigationModeFeatureFlag.java
index 351adf4..c527be3 100644
--- a/quickstep/src/com/android/quickstep/util/NavigationModeFeatureFlag.java
+++ b/quickstep/src/com/android/quickstep/util/NavigationModeFeatureFlag.java
@@ -46,7 +46,8 @@
     }
 
     public boolean get() {
-        return mBasePredicate.get() && mSupported && mObserver.isHomeAndOverviewSame();
+        return mBasePredicate.get() && mSupported && mObserver != null
+                && mObserver.isHomeAndOverviewSame();
     }
 
     public void initialize(Context context) {