DO NOT MERGE Add null check for status bar transitions

Test: atest SystemUITests
Bug: 150570478
Change-Id: I4c93a08ddcbe35a95b77012e2345bfa25167be1b

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

@@ -2277,8 +2277,10 @@ public class StatusBar extends SystemUI implements DemoMode,
 
     void checkBarModes() {
         if (mDemoMode) return;
-        if (mStatusBarView != null) checkBarMode(mStatusBarMode, mStatusBarWindowState,
-                getStatusBarTransitions());
+        if (mStatusBarView != null && getStatusBarTransitions() != null) {
+            checkBarMode(mStatusBarMode, mStatusBarWindowState,
+                    getStatusBarTransitions());
+        }
         mNavigationBarController.checkNavBarModes(mDisplayId);
         mNoAnimationOnNextBarModeChange = false;
     }