Fix SysUI crash on device boot.

Bug: 22869066
Change-Id: I55ab64c430899ebc20bfc8a8e4d1e2a7cd12f0cd

Author: Julia Reynolds

packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarView.java

@@ -370,16 +370,18 @@ private void setLayoutTransitionsEnabled(boolean enabled) {
         mLayoutTransitionsEnabled = enabled;
         ViewGroup navButtons = (ViewGroup) mCurrentView.findViewById(R.id.nav_buttons);
         LayoutTransition lt = navButtons.getLayoutTransition();
-        if (enabled) {
-            lt.enableTransitionType(LayoutTransition.APPEARING);
-            lt.enableTransitionType(LayoutTransition.DISAPPEARING);
-            lt.enableTransitionType(LayoutTransition.CHANGE_APPEARING);
-            lt.enableTransitionType(LayoutTransition.CHANGE_DISAPPEARING);
-        } else {
-            lt.disableTransitionType(LayoutTransition.APPEARING);
-            lt.disableTransitionType(LayoutTransition.DISAPPEARING);
-            lt.disableTransitionType(LayoutTransition.CHANGE_APPEARING);
-            lt.disableTransitionType(LayoutTransition.CHANGE_DISAPPEARING);
+        if (lt != null) {
+            if (enabled) {
+                lt.enableTransitionType(LayoutTransition.APPEARING);
+                lt.enableTransitionType(LayoutTransition.DISAPPEARING);
+                lt.enableTransitionType(LayoutTransition.CHANGE_APPEARING);
+                lt.enableTransitionType(LayoutTransition.CHANGE_DISAPPEARING);
+            } else {
+                lt.disableTransitionType(LayoutTransition.APPEARING);
+                lt.disableTransitionType(LayoutTransition.DISAPPEARING);
+                lt.disableTransitionType(LayoutTransition.CHANGE_APPEARING);
+                lt.disableTransitionType(LayoutTransition.CHANGE_DISAPPEARING);
+            }
         }
     }