Adds null check for proximity wakelock

Bug: 11319677
Change-Id: Ie62144dc5a738bb294a802230dce7847f734f39e

src/com/android/incallui/ProximitySensor.java

diff --git a/src/com/android/incallui/ProximitySensor.java b/src/com/android/incallui/ProximitySensor.java
index 5776b56..607a54f 100644
--- a/src/com/android/incallui/ProximitySensor.java
+++ b/src/com/android/incallui/ProximitySensor.java
@@ -73,7 +73,7 @@
 
         mAccelerometerListener.enable(false);
 
-        if (mProximityWakeLock.isHeld()) {
+        if (mProximityWakeLock != null && mProximityWakeLock.isHeld()) {
             mProximityWakeLock.release();
         }
     }