How to unpause the thread in my Android surfaceview?

How to unpause the thread in my Android surfaceview?

I actually can pause the thread correctly but when I press the unpause
button it force closes. What am I doing wrong ?
public void pause() {
mRun = false;
while (true) {
try {
_thread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
break;
}
_thread = null;
}
public void unpause() {
mRun = true;
_thread = new GameBoardThread(this);
_thread.start();
}
here is the logcat after pressin my unpause button
08-14 09:17:51.272: W/dalvikvm(328): threadid=1: thread exiting with
uncaught exception (group=0x4001d800)
08-14 09:17:51.352: E/AndroidRuntime(328): FATAL EXCEPTION: main
08-14 09:17:51.352: E/AndroidRuntime(328): java.lang.NullPointerException
08-14 09:17:51.352: E/AndroidRuntime(328): at
com.gimi.infinite.car.GameBoard$GameBoardThread.pause(GameBoard.java:210)
08-14 09:17:51.352: E/AndroidRuntime(328): at
com.gimi.infinite.car.MainActivity$1.onClick(MainActivity.java:46)
08-14 09:17:51.352: E/AndroidRuntime(328): at
android.view.View.performClick(View.java:2408)
08-14 09:17:51.352: E/AndroidRuntime(328): at
android.view.View$PerformClick.run(View.java:8816)
08-14 09:17:51.352: E/AndroidRuntime(328): at
android.os.Handler.handleCallback(Handler.java:587)
08-14 09:17:51.352: E/AndroidRuntime(328): at
android.os.Handler.dispatchMessage(Handler.java:92)
08-14 09:17:51.352: E/AndroidRuntime(328): at
android.os.Looper.loop(Looper.java:123)
08-14 09:17:51.352: E/AndroidRuntime(328): at
android.app.ActivityThread.main(ActivityThread.java:4627)
08-14 09:17:51.352: E/AndroidRuntime(328): at
java.lang.reflect.Method.invokeNative(Native Method)
08-14 09:17:51.352: E/AndroidRuntime(328): at
java.lang.reflect.Method.invoke(Method.java:521)
08-14 09:17:51.352: E/AndroidRuntime(328): at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-14 09:17:51.352: E/AndroidRuntime(328): at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-14 09:17:51.352: E/AndroidRuntime(328): at
dalvik.system.NativeStart.main(Native Method)
08-14 09:17:54.723: I/Process(328): Sending signal. PID: 328 SIG: 9