SystemServer: Fix null pointer exception

E/System  ( 4271): ************ Failure starting core service
E/System  ( 4271): java.lang.NullPointerException
E/System  ( 4271): 	at com.android.server.BatteryService.<init>(BatteryService.java:192)
E/System  ( 4271): 	at com.android.server.ServerThread.initAndLoop(SystemServer.java:348)
E/System  ( 4271): 	at com.android.server.SystemServer.main(SystemServer.java:1406)
E/System  ( 4271): 	at java.lang.reflect.Method.invokeNative(Native Method)
E/System  ( 4271): 	at java.lang.reflect.Method.invoke(Method.java:515)
E/System  ( 4271): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
E/System  ( 4271): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
E/System  ( 4271): 	at dalvik.system.NativeStart.main(Native Method)